Online Learning (LMS)

Budget: $1,000 to $2,500

I am looking for a developer who is familiar with online learning systems. We want to build a site that will allow students to take an online test and print out a certification after they take the test. The student will pay after they pass and before they print the certificate. The test must be auto refresh so they can't take a repeat test. It will need to have the capability to add images and videos, and communication with the instructors. It will be updated by the administrators. To keep costs down it can be an open source program.
Only respond if you have experience and references please.