Sometimes we are undecided between a couple of camera models.
The best thing for figuring out the differences and picking the winner is to go to the manufacturer's website and compare the specs. If they are made by the SAME company, you may even find a comparison tool right there on their website.
Carefully read the specs and make note of the differences.
Make sure to get a camera with manual modes (manual, aperture priority and shutter priority), so you have the choice to be as creative as you want to be. Don't worry..... the old AUTO function will still be there, too, just in case you can't cope without it.
Nearly always the newer and/or more expensive model actually IS the better one, too, but that doesn't necessarily mean that you really NEED the dearest one. This is the part that is hardest for us to answer, since YOU know much better what your needs are than we do.
If you're still undecided, google for a few reviews and check out sites such as www.dpreview.com or http://snapsort.com/compare
Doing this work yourself instead of waiting for an answer to be presented has a big advantage for you. It forces you to do some thinking, research and learning. In the process, you become an educated shopper who is much more likely to enjoy his/her purchases instead of regretting the wrong choices a short while later.
Enjoy the journey - that researching part can actually be fun!
About the video part: Many still cameras have video functions, and especially the DSLRs with video produce decent enough results. However, if video is important to you, you are MUCH better off with a camcorder.
At this point in time, they still do a much better job (and are much more user-friendly) at video and audio recording than still cameras can.
P.S. 300- 450 WHAT????????????? Pound or Euro or Dollar (which one?) or Baht or Francs?There are hundreds of currencies in the world..... and boy, do they vary!
It sure would help if you told us which currency you are speaking about.
Since you didn't bother to specify, I will assume you're talking about USD.
Your budget is VERY low, at best you'll find something with a basic kit lens but you will have NO money for any of the extra bits and pieces you'll want/need, let alone more lenses.
You might be better off looking for a bridge camera for that sort of money.