Of the 3, BuyDurangoRealEstate.com is probably the most valuable. I checked around and most of the other major cities versions of that domain are taken, so it is popular. Undeveloped, I can't see it going for more than a couple hundred bucks (maybe), because there are lots of alternative domains people can buy.
DurangoColoradoRealEstate.com is probably worth close to the same... The main problem is they are both so long, but they do have good keywords. Your best bet would be to build a couple mini sites and try and sell them that way. Just some basic layout that a realtor can easily put together a nice site. Both domains will probably take some direct marketing to Durango Realtors to be able to sell.
As for DurangoRealtors.net, Realtors is a trademarked word and it is a dotnet, both bring the value way down. You might be able to get $100 for it (if your lucky), but I would rather have DurangoRealtors.biz or DurangoRealtors.info myself.
I checked out your site DotWords.com (That's a good domain), and of all your domains, I like WebNewbies.com the best.