Free: Contests & Raffles.
The ones I have looked through I would say Vortex. Get a hold of Elknut, he is great to deal with. I just ordered my Vortex PST rifle scope from him.
Vortex Nomad is the best for the money hands down. Best warranty there is. if it brakes they will fix or replace even if you whack it with a sledge hammer on purpose! Don't have to be original owner and don't need proof of purchase. No one else can even come close to warranty. Optics shatter anything in the field for the same price. Talk to the guys at Sportsmans and Wholesale Sports and they will all tell you the best glass for the money hands down no comparison at all! I think they around $250-$350 I cant remember which.
The best spotter for $500 is going to be a used one.