Do NOT buy a pool table online.
I don't care how nice they look in pictures, you have no idea what you're getting if you're not familiar with the particular brand you want. 99% of what they sell online is complete junk anyway, so it's hardly worth even looking.
Watch the local newspaper for sale ads for local table dealers, often times you can find very good sales, especially on floor models. You may be able to find an excellent valued table in your price range if you're patient.
New vs Used: If you have a keen eye, you can get a great deal on a used table. If you don't know what you're looking at, stick with major name brands (Brunswick, Olhausen, Connelly, etc) and just look for very low prices.
The biggest drawback to buying used is that you're almost always going to pay more than you think. You'll almost certainly need to replace the cloth, and if it's more than a few years old, will probably want to replace the cushions as well (if you want it to play like it's supposed to). You will probably need to rent a U-Haul to move it unless one of your brothers drives an F350 or has a flatbed trailer. So tack on at least a few hundred dollars to list price and compare it to a new table, you might not be getting a very good deal used if you're not careful.
Putting a table together is not as easy as it seems. Man power is no replacement for know-how. It might take you a week to put it together instead of a day, and even then it might not play correctly. Now, if budget constraints demand that you put it together yourself, then that's certainly what I would do, but the money you're going to spend is well worth it IMO.
You will have to pay a decent amount of money to have it delivered and set up. $500 seems a little much, but $200-$300 should be budgeted for delivery and setup of a new table. Some places will have "free delivery and setup" sales, so watch for that if you want to save some money.
Balls and cues may or may not be included with the table. Brick and mortar stores will almost always wheel and deal and either give you these for free or have a cheap set you can buy. Obviously, these types of sets are substandard for serious players, but let the next guy who's a serious player buy himself a set of Aramith Super Pros and if anyone wants a better cue, they can buy their own. Chances are the ones hanging on the wall at your frat house will get beat to he11 regardless of their quality.
Before you do anything, go to a table store and talk to a salesperson about what to look for in a good table. If you buy new, you should lean towards name brands, but there are certainly some good quality local companies that may allow you to save a lot of money. You may be able to get a solid wood table with 1" slate for the same price as a name brand table with veneered woods and 3/4" slate. My only warning about dealing with the salesperson is to try and avoid getting talked into too many unnecessary "upgrades." Simonis cloth and Artemis cushions are nice, but pricer and probably not worth the added expense when 90% of the players are not serious and won't care that much, and given that a pool table in a frat house is going to get excessive use compared to a home table.