here in Matiguas Nicaragua bandwidth is really expensive but 500km away (line of site from mountain near by) is Costa Rica with decent infrastructure and decent prices.
considering the following it should be possible to do a link
transmit power 500mW 24db
antenna gain send 36dbi
antenna gain receiver 36dbi
free space loses at -160db
that leaves -64db at the receiving end, enough for a stable link, assuming the Fresnel zone is free