What is the difference between a regular xbox360 console and the xbox360 arcade console? And what stores have the best prices?

The arcade version does not come with a hard drive. The prices are usually about the same no matter where you go. You might find a sale at one place if you keep an eye out but the price never usually changes. In my opinion, get the normal 360 just for the hard drive the extra money is worth it for the amount of stuff you can put on the hard drive.