How much can you COMFORTABLY spend? I say "comfortably" because you will likely need money for supplements to treat the AF, and they average out to about $1.30 a day.
I don't think one saliva test/lab is better than any others. Your readings will be your readings, they are hard numbers and you will have to come back here for us to interpret them (or in Lam's forum, since that is one of the things he is actually GOOD at, j/k.)
Check out the four companies in this link and look for the most inexpensive test. All you want to check is DHEA? What about cortisol, do you know about it?