as has been said corny (pepsi/coke kegs) are easier for home use. and the kegs used generally only go for $30-40 in the US (morebeer.com, kegconnection.com, ect.), which is really one of the least expensive parts of the setup. for a keg setup you will also need a fridge, which you can find old ones for free if you have the space, or you could spend hundred dressing up a fancy kegerator. And a co2 system $100+ for tank, regulator and lines, this is the biggest cost of a budget system, can be tough to find used, and is required for your beer to last more than a few hours.
overall you can put together a basic system for $150-200 with out to much trouble, if you do a bit a scrounging. but i would not plan on anything much less than that, unless you get lucky.
now if you want a party keg, that one on craigslist would be great with a hand tap and bucket of ice for a few hours. you could carb with sugar just like in bottles and take it with you. but a hand tap makes beer oxidize pretty quick.