I use Model Mayhem a lot. It works well for the most part although I get a number of no-shows and last minute cancellations. Generally I plan to do three shoots on the same day and expect at least one no-show.
For normal commercial work I pay $75 for a two-hour shoot, sometimes less for models with no or limited experience. I do some fine art nudes that I typically pay $200-$300 for two hours depending on experience.
I also try to get people I meet in public and offer TF. That works sometimes but cancellation/no-show percentage is probably 75%.
Some people swear by Craig's List but I've had no luck that way.