Digital
Audio
Workstation - basically software used to record/edit audio on a computer, examples are things like Reaper, Cubase, Logic, Pro Tools, Sonar,
Studio One etc. if you've not gone one/not got one in mind i'd suggest looking at Reaper as the free trial is 30 days and the full licence is only $40 and will do pretty much everything that all the others will for a fraction of the price.
Is it just an upright piano you plan on recording or digital piano through an amp/line output?
I do completely appreciate the joys of being a cash strapped student but in terms of quality over cost there are other avenues i'd explore before purely going down the USB mic route, especially for recording piano which has such a wide frequency range. the benefit of having a separate preamp & convertor (which is basically a stripped down interface anyway) and a separate mic means you're not limited to one product. one of the big complaints about all in one USB mics is that if you don't like the mic you have to replace everything in order to get a different mic, whereas with separate parts you can easily replace just the mic or just the interface. one of the other problems that some people come across are the length of USB cables, whereas with a separate interface and mic you can run a pretty long usb cable from the computer to the interface and then a pretty long XLR cable from the interface to the mic.
As a cheap and sturdy preamp and A/D convertor the
Blue Icicle is great and only £40 (sorry, uk based, $'s mean nothing to me) and in terms of mic's things like
the MXL 990, sE X1,
Shure SM57,
Blue Encore 100 are all dirt cheap and very usable, although for piano recording i'd look more towards condenser mic's over dynamic mic's as they tend to have more sensitivity, although any of the four i've mentioned would wield good results.
If you really can't stretch or save and really just want to get on with recording, which is completely fair enough, then out of the usb mic range the Blue Snowball, Blue Yeti and AKG Perception 120 usb are all ok, but it can end up being a false economy if you find that they don't sound as good as you'd like as you find yourself buying more gear to replace it rather than just adding gear to upgrade it