American voice over

I am looking to get 5 voice overs done for a medical elearning programme. I have the first section script that is around 2000 words long describing the anatomy of the foot. If successful with these first 5 sections which make up 1 module (seen as utlimately one job) there are another 4 modules each with approx 5 sections to be done in the future with the same voice over artist. I have a budget of $500 to cover the voice over for all 5 sections for module 1.