Depends on the condition of the bike you are bolting the free radical on to. Related to my adventure of converting my early 90's mtn bike into an xtracycle, I got a bad case of upgrade disease.
My shifters were starting to slip, so I had to change those out. New shifters weren't going to work with the old cassette, so I had to upgrade that. Old hub wouldn't work with new cassette, so I got a new back wheel (hell, I found a good price on a set, so I upgraded both wheels). Of course old derailleur wouldn't work with either shifters or cassette, so I upgraded that. My old center pull brakes wouldn't work either, so upgraded those as well (just in the back, however got new kool stop pads for the front).
Oh, and the seat? Had to upgrade that as well, since I was riding a heck of a lot more than I used to, and the standard seat on there just wasn't cutting it. Then might as well throw on a new set of grips, new lights and some bar ends.
That lasted me about a year until the BB cut out on me, so as long as I was replacing that, I decided to replace the crank and front derailleur at the same time. I think the only thing I didn't end up replacing was the fork (which I wanted to do so I could put some disc brakes on there).
So......as long as you can commit to ONLY adding on the xtracycle and only the xtracycle, you'll be good to go. If you can't do that, might as well see if you can extend your student loan.