Whether it is through exclusive contracts--Carolyn Murphy must have made bags of money so far as the face of Estee Lauder or other means, some well known models have done quite well.
Maggie Rizer made enough for her stepfather to gamble away a few million;
I have seen estimates of Shalom Harlow's wealth around CAN$ 15 million;
Carmen Kass seems to be quite well off, investing in property in Estonia and such;
but I would imagine that most models are like boxers, another group of freelancers who make their money with their bodies--they don't get paid much to start out and when they do start earning most of their money goes to (in the case of boxers) gym fees, trainer, manager, expenses. Same for models.
A boxer might win a fight with a winner's purse of $50,000 and wind up with $5,000 in cash.
Professionals in each have very little time--usually several years--to make it or find another line of work.