Depends on what you want to accomplish.
If all your after is to make it look nice on the outside, you can do that on the cheap, marine plywood beaded by your local lumber mill, lumber yard, some simple casings for the window, and a good coat of paint.
If, one the other hand, you want to restore it, and put it to use as a open to the public display or a office, your in for a world of hurt.
That sheething is either ash or oak, not cheap.
Skeets was right on, count on whats under that old stuff being in sad, sad shape.
Which means if its a steel frame and sidework, you need to hire a good welder, and they aint cheap by the hour…unless they are a railfan too.
Here is a idea, go back and take a good look under the sides, then decide.
Keep in mind you can form a tax exempt non-profit group to do this also.
The “Save the Caboose” fund…you can get the paperwork from the IRS website, free download.
Then get the schools woodshop and metal shop teachers to take a look, they make be able to help make it a shop project.
Heck, get the cheerleaders to have a car wash, split the proceeds, hit up local merchants for suppliesand donation, they can write it off their taxes, you can put their name on a comemorative plaque on the side, you might even find free labor that way too.
Hit up your local NHRS, they may be able to pitch in knowledge and labor.
But be prepared to spend a lot of your time on it, every time you take some thing off, you will find the part that it was bolted to needs to be replaced/repaired also.
Did way to many 1950s cars, I can promise you the damage is a lot worse on the inside that it looks like from the outside.
So, the real question you have to ask yourself is, how valuable is my time, and how much of it do I want to spend on this.
If all you want to do is make it pretty, you can do it in a month of weekends.
If your trying to restore it, and its just go