Classic Winnebagos & Vintage RVs

Looks like my front ac will get replaced since it kicks the breaker and not cold even when it does run, it being an 1982 almost impossible to find someone to service it and way expensive if I could! My question is what is a good replacement I have seen them from about $500 to over $2000 and the 500 sounds best to me but want something that works good.

I see air conditioners advertised all the time in the Good Sam flyers in the mid 400.00's.