You can save money buying a Mac mini instead, it provides similar performance when connected to cheaper aftermarket monitors, keyboard and mouse. (you do have to buy a separate monitor adapter cable) you won't even have to cast aside a lame 1 button mouse (a mini comes with none).
You can save another $250 or so taking your chances with a used late model mini (look for system 10.6.8) http://www.powermax.com/parts/code/PM_CU_MM_IN
In your situation you probably can't afford to be so picky, a cheap PC might be 1/2 the expense, the cost of legitimate software is probably more than a cheap computer, you can find poor photoshop alternative for free, like Gimp.
There is alternative online work that would still require some sort of computer:
Although I have limited direct experience with the worker side of it, I am always suggesting the one looks into freelance marketplace sites as a way to e********y more immediately than tackling some online business scheme, these include elance.com, freelancer.com and odesk.com, while more geared for technicians, you also can earn about $5 for writing a 450 word article for a web site, while there is worldwide competition, a native English writer has a big advantage. There is usually no sign up cost for workers, employers pay a percentage to the sites, to see how non technical some of the short term jobs can get you might look through the Anything Goes section of the Freelancer job listings.
Odesk which reports it's workers earning some $23 Million in one month, recently projected that online workers may earn a total of $1 Billion in 2012.
Elance gives a nicely detailed report on their worker earnings, including a ranking of most in demand skills.
There are also micro task sites that pay small change for a few minutes work, popular with 3rd world countries, some in the U.S. do them instead of crossword puzzles, the original was created by Amazon, the online store to 'automate' tasks a computer couldn't do, like pick the better of 2 pictures, they named mturk.com after the 18th century Mechanical Turk chess playing machine that had a man hidden inside, shortTask and microworkers have similar micro tasks, some individual jobs are a bit shady, like signing up for product trials, doing surveys, but you get to choose which tasks to perform.