Purpleport is a hosting site for models, photographers, makeup artists, hair dressers etc etc. You can join free of charge and have limited access to all it offers and you will be able to find models with varying levels they shoot to that you can pay by the hour/day etc or if a model wishes to update or build a portfolio you may have an agreement between you both that you will provide a given number of images for her time. https://purpleport.com/home/
There are a few other similar sites but I actually like the format of Purpleport.
Personally I've never had to pay a model from an agency, but I wasn't cold-calling out of the blue. Having a team in place (styling/hair/mu - all working TF) helps a lot though, as is having a style that fits their boards.