Stud fees can vary. Naturally a Supreme Grand Champion stud cat is going to command a much higher price. You definitely MUST have your stud checked for all the medical issues: PRA, PK, HCM, FeLV, FIP, etc. Those tests are not cheap. A Color test is also recommended so you know what type of kitten your stud is capable of producing.
Now on the other hand, you must insist that any queen your stud is mated with has gone through the same testing. Inspect the cattery completely and verify that no other cat in that cattery has any medical issues. I say this because some queens and studs have developed medical issues and died at the other cattery. Yes, most matings go well -- but there is a slight chance there could be a complication if you do not do your research on ANY breeder that wants your stud.
There are also ways to negotiate the fee -- many ask for the pick of the litter -- or female. However, inbreeding continues to this day and I've seen fathers bred back to their daughters and in one case, the father is the grandfather on both sides and the great grandfather on one.
You will need to determine your fee based on your costs, including transportation. AND lastly, a contract its extremely important. You may find samples online.