How many separate tracks do you want to be able to record at one time? Like GazEcc said, most mixers with A-to-D converters have stereo (2 tracks) output. Do you want to be able to DI guitar or bass? Make sure you get something that has the preamp for it.
Mixers for live performances and audio interfaces don't necessarily coincide. I haven't seen any low-end mixers with Firewire (they are typically USB).
I've got a Mackie ProFX12 I love for home use - it lets me plug all my stuff in at one time, no swapping cords out - and it has a stereo USB output, which works for me as I am never recording more than 2 separate tracks at one time. You can get it within your budget if you shop the sales - GuitarCenter always has coupons and deals, even if you can't stand the place!
Don't forget that you are going to need monitors and tracking headphones, too.