If they are still available, then yours is just a used coat, probably worth about 1/2 of what they are selling for now.
If it is from a one time issue, collectors' type item, then it might be worth more than you paid for it, depending on whether you can find someone that wants it more than you to keep it.
Probably a small market for it. But there are at least a few avid fans of the RR that would be interested. As is usual, e-bay (or one of the other online auction places) is probably the best way to reach the widest audience. I assume there is a "friends" organization for the place and they probably have a web presence and probably have a forum that you might be able to advertise on. A search of the web would reveal them. Of course, you probably would need to know about what price range you want for it... and that is probably why you asked here!
What kind of coat is it? A good leather jacket can get $200 or more, retail. A Wal*Mart cloth winter coat would be less than $50, even with some sports logo on it. You will need to supply some photos of it. If you join this site you can post for sale items and I think this would fit the general classification of what is allowed to be sold here (but NOT my decision about that, check with Shad, the forum owner).
Do a search of e-bay to see if you can find similar products, that would give you some idea of price... and it could put dollar signs in your eyes or severely disappoint you!
There is always some one looking for these types of Items. The coat could have been a special issue for a safety award by the RR. Years ago several RRs did this as I have one from the MoPac I received in 1976 for having the best safety record for a division. The coat could have also been just issued to your dad for having over 30years of service with out an injuriy I'd try e-bay if you really want to sell it. Later RJD
Well a lot depends on the scarcity of the item and it's quality.
You said it's in perfect shape so that's one good point for you. The other good thing is that Rio Grande clothing items are relatively rare when compared to other western railroads. In fact the only clothing item I recall seeing in recent times on eBay was a yellow vest that I think had Rio Grande lettering on it. It was listed as a Rio Grande item but I can't remember if it had lettering or not. And I can't really remember the price either, but I think it went for around $45.
Do you know if your jacket is a Conductor's jacket? If so it would be pretty valuable. It would look somewhat similar to this: