You do need to use a dechlorinator on your tap water. They have modified gills and chlorine and chloramine will burn them. It's often sold in the fish area of your local Petco/Petsmart. Something without stress and slime coat is best. I like Top Fin Dechlorinator.
You have no need to bathe them as the poster above said. As long as both water bowls contain enough water for the crabs to bathe themselves, there's no need for you to take them out to do so. If you do decide to bathe them, don't just dunk em in the water for a minuet or two. Give them a nice little tub with plenty of toys they can stay on if they don't fell like taking a dip.
You bought them from a mall, I assume that means you got the crabs in a small plastic tank with a nice little sponge and some pellets to go along with it? Hermies need more than that. Mall kiosks and coastal tourist shops often take pretty horrible care of their crabs and spread misinformation around(the absolute need for bathing to be one). The start up costs won't be cheap, in the triple digits($130+). If you don't think you can/don't want to handle it, you can always put them up for adoption on HCA(first subsection, no registration required) .
more than this.
The 10 gallon(absolute minimum tank size) tank itself should run you around $10-$15. If you don't want to spend money on a the tank, you can always go to Craigslists and see if you can pick one up for free. Garage sales are another good place to find them for cheap.
An under tank heater should run you $21. An 8 watt will heat a 10 gallon tank sufficiently. A heat bulb around 35 watts will heat the tank as well. You can pick one up at a home department store for cheap. If that bulb wattage will not heat the tank sufficiently, you can try going up the size just above. Lights might have a bad effect on your humidity if you get a ridiculously high wattage. This is a link for an under tank heater.
Eco Earth is a very cheap substrate, one brick is $5 and should be sufficient enough to fill the tank(online it's cheaper). Expand it in pre-made salt water to help prevent mold, moisten as needed(poke a hole in the corner and gently add water). This is a good EE deal.
A bag of play is another cheap substrate that you can use. One 50 pound bag is usually $4-5. This can be moist or dry. What ever you prefer. Fine coral sand and aragonite sand are good options too. They only draw back when compared to play sand and EE is that it's more expensive.
What ever you choose, the general rule for substrate is to have it be at least twice as deep as your largest crab.
You will need aquarium grade sea salt for your hermies(yes ALL hermies should have access to salt water). You should use salt made for marine aquariums and nothing else. Hermit crab salt water packs don't hold salinity well. Something like Instant Ocean will work. A 5 gallon bag is only around $5-6 and will last a good while.
Here is a link on how to properly mix salt depending on brand.
A simple hydrometer can come in handy, but it's not required.
A dial or digital thermometer and hygrometer(or a combo of the two) will be needed to measure the temperature and humidity. Any home improvement store should have a cheap combo with not metal attachments. The dial combo in this link will do the job as well, but calibrate your hygrometer as needed(here's a link of it
Your humidity should be between 75?4?Misting your tank can increase your humidity, but it's a pain to keep doing it. Make a little hold in the corner of your substrate, and add water. Moist substrate should keep your tank's humidity good. Moss pits are great for humidity too. Hiawatha moss is good for them and can be found at craft stores. Get a little plastic basket with good quality suction cups(if you're worried, aquarium silicone sealant is safe to use as a glue) and stick the moss there. This is on moss.
A DIY humidifier like this one can help as well.
You do need a container for your food. You can use anything like a peanut butter cap or clam shell. As long as it's not metal. For the water you're going to have to find something that allows your crabs to add water into the shells easily(or bathe basically). I use a small plastic container for my salt water(it has some large rocks because it's too deep on its own)and a reptile dish for fresh. You can use one too, but a reptile water bowl will be sufficient as well. If you have a large tank, you can use a good sized Tupperware(only in large tanks).
You can decorate your tank with just about anything. Most all my decor comes from a dollar store(the used fish cave is probably the only thing that doesn't). Here's a list of some stuff you can use for decor(from my head mostly).
coco huts(you make them yourself or buy them)-hidey
legos(you can make some nice things if you're good with them)-hidey and climbing
A shower caddy makes a good second level
moss pit(oodles of fun for the burrowing hermie, but never use it as a substrate)-humidity
log(none collected outside please)-hidey and climbing
a plastic basket-climbing
reptile/fish caves(some hamsters hideys like igloos are fine as well
a rock wall-climbing
organic bromeliads(WARNING-they probably won't last long) The hermies will probably destroy them quickly. Anyway it's a nice treat and climbing toy(if it's big enough). :3
plastic containers(if you got a tall one, you could fiddle with it to make a hidey/climbing toy)
Strong suction cups(maybe some sold for fish tanks, weak ones don't hold up well) and aquarium silicone will hold just about anything in your tank.
Your hermit crabs should be given a varied diet. They shouldn't be forced to eat those little bottles of commercial food. Meats(seafood, a bit of occasional beef, insects and other inverts,etc...), veggies(broccoli, carrots, spinach, etc...), and fruits should all be included in their diet. This website will give you a good idea on what they can eat and some basic food groups. Your crabs might not try something the first time, don't worry. Just be patient, and they should try the food on their own. You might be able to coax them if you mix the new foods with an old favorite.
This link is pretty good for safe ways to cut costs.
A few times every year(depends on size) your crab(or crabs if they have a molting party >-<) will molt or shed their skin. Normally a crab will find a nice spot underground(they may be in and out during this time) and begin the process. It takes anywhere from a few weeks(normally for smaller crabs) to a few months. Don't disturb them unless necessary(mold grows on the substrate, you find mites or ants in the tank).