How much someone would charge to train and develop a model?
At least a slight introduction to the direction of the model you want to make and basic information that can be revealed is needed.
It's like hiring a tutor, language, literature, history, science...., at least let the maker know what you need
Fiverr is full of people offering to train LoRAs. Maybe some of them are open to train full models as well but you have to approach them individually. Just go to their website and search for "stable diffusion".
There's also someone offering to build a whole "Generate your own AI images online"-service, although it comes at a price: https://www.fiverr.com/vagludir/build-stable-diffusion-ai-saas-app . Maybe there are others that do it for cheaper. Just search for "AI SaaS"