$90 seems a bit steep for a frame that's seen so much wear without its matching fork. I guess it depends partly on how many spare parts you have lying around and what you'll still have to purchase to build the bike up. Add: headset, bb, cranks, cogs, wheels, tires, tubes, seatpost, saddle, bars, stems, levers, brakes, and cables and you could roll that up into a lot of money for a bike that's seen many miles. You can get a Surly Steamroller complete for ~ $650:
http://bicyclebananas.com/mm5/merchant.mvc?Screen=PROD&Product_Code=Surly_Steamroller
If you've got most of what you need already and that $90 gets you most of the way there then I might consider it, but I suspect you can do better if you shop around a bit.
BTW, Sheldon's site (we miss him) has some very good pages dedicated to fixie conversions that you should probably check out in addition to the cold setting link above.
http://www.sheldonbrown.com/fixed.html
-Dave