We have two bulls going to stud in the next couple weeks. One to Genex Hawkeye West at Billings and the other to Alta Genetics, Balzac, AB. While there is some variation in prices between studs, I would be very selective in which one you chose, and don't just use the cost per straw to decide that. There are certain studs that I would never send a bull I owned to even if they offered to collect him at no cost.
Hawkeye West charges $2/straw for 500 doses or less and 1.65/ straw for over 500 straws. Board is $6/ day. Health tests are extra and usually run $600-700 if you are collecting CCS qualified semen ( ie: semen that can be exported to several other countries) If you are collecting semen for use in your own country and are not interested in any exportable semen, the vet costs are minimal.
Alta Genetics is $2.25/ straw and $12/ day board. They are an excellent stud and I do not even consider the additional costs as being significant and they look after your bull and he will probably come back in excellent condition. I have seen bulls coming out of some other studs that have been in very poor condition.
Talk with the different studs and also talk to people who have used each stud as well. I would agree that you should get any promotional pictures taken before the bull goes to stud. Also make sure the stud only processes the highest quality semen possible. I would rather have a collection of 25 good straws than a collection of 100 mediocre quality straws. There is nothing more frustrating than getting some phone calls from people who tell you they had very poor conception from the semen you sold them.