Caddx is an interesting option. i can't find a spec on the open air range, but it appears there is a quick bridge repeater that i could use to help with the 500+' range.
do you know of a caddx unit with an detached antenna that i could mount outside the house?
the repeater doesn't seem like it is designed for out door mounting though.
also, i haven't seen any key/car remotes that are 2-way(not a hard requirement, but seems nice).