Help me understand what I need

So I'm a bit new to this whole wireless networking world. I have experience with Backtrack2, ndiswrapper, kismet, aircrack-ng suite, etc. so I know some of the basics on the software side.

What I'm trying to do is set up a wireless card that can go as far as the FCC regulations allow, without costing a lot of $. For the sole reason in having a fun wifi project, and see how far I can get a connection from. The antenna will not initially be connected to an access point, but I may down the road if I want to find use for the antenna. I plan on having the antenna hooked up to a computer for use. Preferably this would be hooked up by USB, but it could be PCI.

So my question is, what am I looking at? How much would such a setup cost? What antenna gain am I shooting for and what transmitter RF power, etc.? Is antenna gain more important than transmitter power for this? How many feet would this be able to shoot, through an average neighborhood with houses and such?