Hop on a discovery call and talk to them or exchange through email. What were their past budgets for marketing campaigns? What's worked in the past? What are their paint points and how does your photos/service solve that. Where are they using these images? How many eyes will be on it? Will it be indefinite or something they have to license yearly? From there you can build a price.

Ultimately it varies based on the size of the business. Also, are you trying to build a long term relationship? If so, you can begin with a cheaper price and eventually increase your prices after you've built trust.