Or if a real parabolic antenna is too expensive, sticking a copper wire on a BNC connector mounted in a Pringles can (5 GHz) or wider tin soup can (2.4 GHz) works as a cheap alternative.
Even simpler would be to take a standard dipole and put a corner reflector around it (not quite as pin-point powerful, but you can still get plenty of gain). You can make these out of roofing flashing.
Would this small device even be able to send data back to the antenna to complete the connection? It might work with a non standard protocol though, where it just accepts data sent to it via 2.4GHz.
Also, the 8 mile range is obviously very theoretical, in a direct line from point A to point B with no obstacles.
"2.4Ghz wifi antenna extends a 7 degree wide cone, allowing it to perform over large distances up to 8 miles of range."