If you are building up an old road bike to fixed, don't buy a front wheel, use the one you have. Use as much existing stuff as you can.

There are plenty of sites that will sell you just a rear wheel for fixed. I got into fixed riding about 4 years ago on a cheapo rear wheel for about $100 US.

I have trashed the cheapo hub (it lasted four years!!!) and have since gotten something better. I can not imagine not having a fixed gear bike now.

Start cheap to see if you like it. Fixed gear is not for everyone but I think everyone should try it!