You probably know this already but if it's the propane
that is not working take out the fridge
, turn it upside down and leave it for a few days. Apparently many of old 3 way fridges can be recovered with this technique.
A new replacement fridge
will set you back $600-700 BEFORE install up here in Canada - I was pricing them this spring. I phoned all the local RV shops and got a wide variety of prices so if you go new that's what I recommend you do.