Err? DON'T want to put you off getting an AI but...
According to this..
Boss BR1600CD
you can transfer audio and MIDI tracks to a PC (or mac) via USB. I say still get an interface because the BR will not do all the things even a modest AI will.
With that last in mind yes, second hand AIs can be a bargain. I have in the past had a Tascam 122 and 144, an Alesis i02 (but they are so cheap might as well get a new one!) and best of all, a Focusrite 8i6 for £100. The latter came without the vital 12volt 1amp wall rat supply but if you see similar use that as a bargaining tool to beat down the price. I had several at home and it does not seem at all fussy what you use.
Considering the BR's facilities I would look for an AI with MIDI and S/PDIF . Other contenders...M-A Fast track Pro and the Native Instruments KA6 although they tend to be keepers!
Dave.