I'm thinking of getting a keg for a party. About how much can I expect to pay?

It depends on what size ( pony or 1/2) and what brand of beer. You should expect to pay around $120 give or take a few bucks, with a tap rental and a tub to put the keg and ice in. This includes a deposit you should get back when you return the empty keg and tap in a timely manner. A premium beer or even a "big" name beer might cost you more. If you are having a large crowd and people who are less inclined to be picky, you can go with less well known brand and pay a little less. Just know that a 1/2 keg will get you ROUGHLY 200 9 oz. gles of beer.