I would say $400 is very reasonable for the prep-work associated with the cabinets. MDF is a huge PIA to paint. A lot of primer, a lot of sanding, a lot of bondo. Materials are cheap. He used automotive paint too (a requirement by me) which can be a bit pricey for good stuff that will last.
If you are in the DC/Northern VA area I have all of the stuff to paint (air compressor, spraygun, etc) and can help you out… if you provide a garage. I don’t have one in the rental house I am in. The house I own in Miami and Groton have one, but not here :(… it really limits what I can do!