I use mccgrp.com to run my checks. ~$40. That includes credit, criminal, past landlord checks and employer checks. The tenant pays the $40.
Be sure to do a county level criminal check, not a "nationwide check" which is not worth .02.
Know what tenant criteria you are looking for, BEFORE advertising. Credit score, income, criminal history, and rental history.
Rely on credit score first, income second, rental history last.
I use postlets.com, craigs, and Rentbits.com (sometimes, it's ~$109).
I typically have to fill 10-12 apartments a year.