I would recommend against almost everything mentioned here other than the taxidermist option.
I was the first person at the university I work at to do fully articulated fish skeletons.
I also do skulls - mainly because they are easier.
I have received offers for my work to be sold in "oddities" stores, but for me the time and effort involved is just not worth it.
Buy yourself some dermestid beetles, now. Id recommend a site, but I cant. Ive seen them before at reasonable prices, so just do some searching.
Standard procedure is to freeze the animal for over 24 hours (make sure theres nothing on there that could hurt the bugs - or at least that is protocol at the university, probably not necessary with fish, but it helps keep the smell down if that bothers you for the next step).
Then clean all of the meat and skin off of the animal - I have a large custom dissection kit that I do this with. I literally scrape the meat off of the bones. This is not just filleting fish.
Then dry your fish out. I have a fume hood - you will probably need a hot, sunny day, a fan, and some way to keep the other bugs off of your fish. Maybe you can get away with this in a basement. You do not want other bugs to get into your culture and kill your dermestids. Magots will be TERRIBLE and DESTROY your skeleton. There is a chance with dermestids that you can keep it articulated without doing all that much.
Next you sit and watch the fish. The process will vary based on how well you cleaned the fish, the size of your dermestid colony, how hungry they are, etc. You need to keep a close eye on this. I usually let fish stay in there for between 24-72 hours for fish that are under 2'. (This does very, and the process is closely monitored)
Before you start to see bones coming loose, you remove the fish from the colony, and pick all of the adult beetles and larvae off that you can. Then you add it to another plastic container, and continue to watch it. In the full colony, the beetles will eat indiscriminately, destroying the things that keep bones together. If you remove the fish, the smaller larvae will go to the "choice" spots and continue eating the meat there instead of just eating wherever they can find a spot on the fish.
Again, after close monitoring, you will remove the fish again, remove all the adults and larvae you can, return them to your master colony, and then put the fish in the freezer for 24 hours to kill the remaining dermestids. Gently tap these into the trash, pick them off, blow them out - whatever you have to do.
Now, at this point, I go to work with that dissecting kit again, probes, tweezers etc - and start removing the little bits of skin that you couldnt, and the beetles couldnt get. By far the longest part of the process IMO. After you are satisfied with this, I add the fish to a solution of hydrogen peroxide that is equal to or less than 10% strength.
This is OPTIONAL - but will seriously help your fish look and smell better. Monitoring at this point must be VERY strict, and in my experience (again on those smaller fish) is that this process is under 12 hours, especially if you want any articulation at the end of it. I recently did a baracuda skull that I harvested in the keys for a spearfishing trip this past march, and went for a LONG time. It got real nasty in there, but man are those bones clean! The skull is also in a million pieces, and I lost a couple teeth. (Luckily teeth are in no short supply in a barracuda mouth
)
Watch it, watch it, watch it. Ive done a small Osphronemus gourami (less than four inches) and only lost a few ribs in a (about) 12 hour soak.
To those who would like your fish preserved. Take a good long look at how skin mount fish look after awhile. In my mind the artificial mounts (all you should need to provide are measurements and a picture) are better looking, last forever, and are lighter to move and mount. Just my .02 - as someone who has done skin mounts and seen a lot of other skin mounts get old.
Ill be watching this thread, and if I can help further I will.