I have had that done to a couple boxes over the years. I don't remember exactly, but $40 plus shipping seems to be the ballpark of what I have paid in the past for a routine tuning.
I had to send my Master accordion to someone last year because when I played in Vegas in 115 degree heat with no shade, the wax got loosened up enough that about 1/3 of the reeds fell out. (The wax didn't actually melt) Anyway, I sent it to Larry Miller, who rewaxed all the reeds, added screws to hold them in place, and did a thorough retuning for $100. It seemed like a good deal to me!
If that happens again you can easily fix that problem yourself. Just gotta put the reeds back where they came, carefully re-melt the wax (dries in a minute or two) and screw the reeds back in. I use a heated "glasses screwdriver" every time.
I guess the Master accordion's reeds were not screwed in? I tell I wouldn't want to be drilling holes to add screws!
Well, things were messed up enough inside that I didn't want to try it myself. There are many minor repairs that I would undertake, but most things having to do with reeds is where I draw the line. In fact, a reed fell out a couple years ago, and I tried to put it back, but somehow it had gone WAY out of tune, so I took it back out and just left it out for a long time.
Also, I had been procrastinating on getting it tuned anyway, so that was obviously a good time to do the whole deal. Larry said that one of the reeds was so bad he had to replace it, but I'm not really sure what that was all about.
Like I said, for $100 and a quick turnaround (like a week) it was totally worth it to have a pro take care of things.
By the way the reeds were not screwed in place before (as you deduced). I didn't know that Larry was going to do that, but I don't mind that he did.
There's a guy name Boaz Rubin who is supposedly a master accordion builder. He now works for Hohner and he did a repair on my Ariette. Not sure of costs as mine was under warranty, but you can reach him here.
Manager, Accordion Department
1000 Technology Park Dr.
Glen Allen, VA 23059
Phone 804-515-1900 xt 3006