hi, im a band with 2 guitars and a drumer.we have 2 mics, one usb and the other 1/4 input jack. what type of interface would be the best bang for our buck? in other words whats the cheapest interface that fits our mic types and would improve our sound over recording directly into a computer?
what kind of mics are they (brand/model)? usb mics typically arent great and mics with a 1/4" jact typically arent either.

you dont need an interface for the USB mic, and for 1/4" there are a few decent options.

what exactly is your budget, and are you trying to record everything at once?
I'd ditch the mics you have and pick up some new ones with XLR inputs.
The problem comes with recording software. Usually the properties only allow you to select one interface at a time so you probably won't be able to record the USB mic while running your new interface.

Two shure SM58 mics are just $200 and you can't beat them for live sound or even some studio situations.

It sounds like you're on an extreme budget. Save up some cash and once you have enough cash, get new mics with XLR connections as well as the interface. I suggest the M-Audio Fast Track Pro.
First off, you might want to say what mic's you are using and do you want to layer or live record it?