I don't think it's unreasonable for a company to require you to put up a few thousand dollars when you start. Think of it from their perspective. If it wasn't required, what's to stop someone from coming in, losing $5k or more of the company's money in high risk trades, and then leaving? Think of it as a security deposit. I'm sure there are shady companies out there that are just trying to get $5k out of you, but don't dismiss a company just because they require some capital up front.
As for those people who are suggesting that you save up and start trading on your own, I disagree. Trading is an extremely difficult skill to learn, and trying to do it on your own is almost impossible. The advantage of working at a prop shop is that you're surrounded by experienced traders that can help you work your way through the learning curve. Don't get me wrong, it's still going to take a long time before you start making enough money to live on (probably about 12 months), but it's the best way to learn.
Before settling on a company to work for, see if they'll let you come in to the office for a day. You want to get a feel for the work environment. You want to be trading in a place where people are working together and helping each other out. If you get the feeling that it's every man for himself, then you don't want to work there.
I started trading pretty much straight out of college, and I don't regret it one bit. Yeah, I had to have a second job for the first 6 months, but it was worth it. What other time in your life can you take such a big risk? If you're like I was, you don't have a house to worry about, and you don't have a family depending on you for income. What better time to take a chance? I say go for it. Just make sure you're getting in with a good company.