If you buy quality used gear at a competitive price, you can usually turn around and sell your stuff if things don't work out, and without really taking a financial hit. Therefore, you can probably spend $2500 on your first set up if you really want to (I wouldn't though). Gear can be a liquid asset.
While I haven't really applied this philosophy to DJ gear yet, I've bought and sold plenty of guitar, bass and drum equipment. When you break even, it's kind of like renting for free. Obviously though, the ultimate goal is to get something your happy with that you want to keep for a long time. It's just reassuring that you know you can convert it to cash if you need to.
Do your homework. Follow eBay auctions and check the "for sale" area of this forum and see what things are going for. On eBay, make sure that the prices your seeing for gear are what they're actually selling for and not what they're listed at. Auctions with several bids tend to end at prices near their actual used value.