It doesn't really sound like an auction - more like a raffle. i.e. If 10 people pay $20 but only one wins it...

I actually looked at making a site like this for selling my house a couple of years ago. Fortunately I did some analysis before building it as in NZ it came under the gambling commission rules. This meant that I could only build a site like this if I donated all the proceeds to charity - unfortunately that was against what I was trying to achieve so never went through with it.