My thought is, if you pay an agent ahead of time what inspiration to do they have to market you? To find your work and to hunt for castings and submit you? They have already been paid so why do they really feel inspired to make you a model? So I would suggest never paying an agent, and now that the Internet is allowing many modeling casting agencies over the web you must be careful or at least cautious when paying to be apart of a modeling website. Some websites charge you up to $50 dollars or more and it might feel nice to have your photo on a modeling, casting, or talent website but be careful. I would first pick up a Ross Reports and try to market yourself to commercial print modeling agencies, or talent agencies who have a record and history of booking work for at least background work on television shows, or at least call or email their talent and send them out on actual castings to companies you have heard of.
The Internet helps to keep us all close, connected and able to dream, but be careful and ask a lot of questions, before you pay a casting website. I don't believe in it, and I think that an agency shouldn't get paid before you do for an actual job.
The only thing you should pay for is stamps and a comp card or headshot. This might mean you have to pay for the printing of your headshot, or to make a comp card, which is normal, but paying an agent, before you get paid is a scam, and modeling scams are no joke!