I think it is $150, after they get things fixed up. I know there was no charge when I got mine, which was 3-4 months ago.
You will need to register here first, at the link below, and then I believe they will send you details.
Network Certification | SolarWinds Certified Professional - SolarWinds
"To begin the registration process, please enter the details below and you will receive an email with detailed instructions, study tips and program details."
I hope it helps, and good luck to you.
-Will