Neil Underwood posted a great summary of pricing options for getting your own RepRap 3D printer. His analysis shows three different price levels, ranging from a full-on everything-you'd-possibly-want version for USD$850 to a very basic, just-enough-to-say-you-did-it USD$350 version. There's also a more practical level at USD$550 for a "realistically cheap prusa model".
Be sure to watch the 10 minute video in which Underwood takes us on a detailed tour of each model, showing the compromises, decisions and interesting points along the way.
And of course, if you're not up to building a RepRap yourself, you could consider buying an assembled version, perhaps from BotMill. But it'll cost you more.