Hi, this is a big one. The 2 best sources are competitors, though you don’t want to compete on price, as that’s a “race to the bottom” death spiral which favours large, established companies.
The other one is to focus on value, not price.
What will customers pay for you to solve their problem, and in what manner? One-off, subscription, PAYG etc.
The only good source of that data of actual or potential customers, so getting front of 10-15 will give you a great idea of what will work in the market. You can do a survey but even a few 1:1’s always helps refine your questions as well as giving good data.