Also, what appliances do you wish to keep back in the 50's or do you want modern appliances in it?
When I was a kid camping with my folks back in the day the little Shasta trailer we had only had an ice box, hand pump sink and a 2 burner propane stove and a single propane lantern type of light in it.. It did have some 120v power stuff if you plugged it in.. A single light and a single outlet..
It would be a venture that only you can do for yourself and there is no way to tell how much it would cost in the end...
Good luck and if you decide to take it on, post some pics of it, as we love that kind of stuff! :)
Mitch