It is going to vary, A LOT!
A couple years ago I got a 16' fiberglass boat painted. It took a little over 2 months and a little over $2k. Half of that was just materials. The same shop does bread and butter insurance work. They also do $10k+ SEMA show cars and full customs.
Since I did the initial body work there was no guarantee on what I had done. I gave them exactly the products that were used so they could check compatibility. The description was I wanted it to look great as it sat on the water at the dock, and good on the trailer. A shiny 5 footer. Spray, fix any runs and nibs. No cut and buff. Once we were on the same page, this isn't going to be show quality but better than painting at home, we were good to go. Another key thing, a deadline. I gave them 3 months. It was done a little sooner. Would have been a little quicker but there was some weather come through town and the boat sat it out until it was better to paint. They also had a little spike in insurance work. Everyone comments on how nice it looks, I know where there are a few flaws. I put a few scratches in it putting everything back in it. I take care of it, but I still take it out and use it.
The work consisted of another coat of sandable primer, and sand it down. 2-part white base coat. Layout a simple graphic (had templets) on the sides and back (basic 2-tone) and put a base/clear metallic.
The final paint is only as good as the prep, and the prep is what takes the time, talent, and money. As much as you think you are ready for paint, it isn't. Flaws that you don't see now will be seen after the paint is laid down. The "we paint anything" shops will paint anything. If you don't want to pay the prep, they will paint over rust, dirt, tape, dead bugs, anything.
One of the bad things is there are a lot of flakey painters. a LOT of them. Too many paint fumes? I've known several people who have been burned by a friend of a friend who will paint it cheap at home. Going over with a trailer a year or so later to try and get the unpainted vehicle back, and figure what parts have been lost in the process.