bobr;
Lots of options then, though I can't say if they will give you the 500 ft you ask for. Here is an X-10 option.
Throwing cost aside I would say investigate the
W800 RF Receiver from WGL Designs and use
THIS antenna with it (placement may be critical for increased distances). Note that the W800 can talk directly to the Elk.
I would also think that a palm pad remote would give you better distances than a small keychain remote, but I understand the reason for the smaller size you request.
PS: Welcome to CocoonTech. I see that Mr. David Steel(er) told you about this place!
