Welcome to the Forum!
I think the price differences between the various kits you're looking at are probably due to one of two factors. Either the dealers bought them at different times, or one is from Revell/Monogram of the U.S.A. and one is from Revell of Germany. The kits imported from Revell of Germany tend to be more expensive.
In any case, they're all made from the same molds. There may conceivably be some differences in the color of the plastic, the amount of flash, and stuff like that; it's possible that the plastic in one will be of a slightly different consistency and hardness than the other. But the parts will be identical in shape, size and number.
My advice would be to take a good look at the boxes, and if you're confident that the cheapest kit hasn't been banged around significantly, buy it.
It's grand old kit, and a fine basis for a scale model. Unfortunately it's been around for quite a while (since 1965, to be exact). I haven't built one for many years, but people who've bought the kit recently have mentioned problems of warping, flash, etc. that almost invariably are found in old kits. You should be prepared to do a considerable amount of cleaning up of the parts. But if attacked with patience and care, this kit can produce a beautiful model.
One other thing to bear in mind. You're going to notice some pretty significant differences between the kit and the ship you visited in Boston. The Revell kit is based on some research the Smithsonian Institution did years ago; it represents the ship as (the Smithsonian thought at the time) she looked in 1814. (More recent research has cast a few doubts on the Smithsonian's plans, but I think they're generally pretty good.) The
Constitution has been modified many times since 1814. During the past twenty years or so the people in charge of her have gotten rid of some of the more obviously modern anachronisms, but they still have some way to go. You'll notice, for instance, that the carvings on the stern of the model are much different from those on board the real ship. There are also some differences in the deck furniture and armament.
There's room for argument about some of these features. If this is your first model, though, and you want it to represent the ship as she looked in her days of glory, my suggestion is to stick with what the kit says. If you want to dive into the archives and do a lot of research you'll probably find some aspects of it that you want to change, but if you build it out of the box you won't go far wrong.
Good luck. It's a great hobby.