In a 2015 paper Ingham (MPI developer) didn’t find a significant difference between his MPI and prolonged speech. More of the prolonged speech participants dropped out, which they use as an indication that MPI is superior to prolonged speech. 5000 seems like a lot to me. There are other options than MPI. Might be worth looking for other options. Ingham is located in SoCal. Are you in SoCal? If so I might recommend you look up Loryn McGill before you commit. She’s a private practice SLP that specializes in stuttering. If that is your only local option it might make sense, but that cost seems high.