if all you want is a beater bike to cruise around on, all you need is any old 10 speed bike, and a prebuilt cheapo singlespeed wheel. you should be able to find a bike for under 100 easy, and the wheel for around 50. done.

strip the derallieurs, shifters, and rear wheel off your bike, pop the new single speed wheel in. Use a chain tool to pop a rivet out of your chain, remove a small section, and refasten it back together.

total cost in bike parts- 150 bucks tops.
total cost in tools (if oyu don't own any yet- adjustable wrench and chain tool. 20 bucks tops.


thats for a budget, beater bike to mess around on. the kind you don't mind leaving out in t he rain when you're at class, or locked up in a high theft area. it probably won't be the prettiest bike, it definitely won't be the fastest out there, or the lightest. it all depends on your priorities, budget, or quality parts.