You can deposit whatever amount you want to, and 
if it's a cash deposit you will be allowed to 
bid up to 5x that amount. However, if you make 
your deposit with a credit card, they will NOT 
charge your card. They will simply authorize it 
for the amount you requested, and you will be 
allowed to bid a maximum of 1x that amount. In 
other words, it really doesn't have to cost you 
anything to sign up. (All of this info is on the 
site. Just click on 'making a deposit' after 
sliding your cursor over 'registration'.)