That's actually really good for consumer grade equipment. Your other options, IMO, would be to buy a pair of commercial grade wireless bridges with high-gain antennae or trench some cable.
A bridge does exactly as it means, connects point a with point b. At the points u run the bridge to a switch or directly to the machine.
Its point to point should be stronger then just hooking onto the wireless at point a.
Linksys has an outdoor grade one that would be about 800 for the pair.
I would try to get 2 wireless routers capable of tomato set up the bridge and crank the transmit power.
If that don't work I'd trench it.
Imo if ur gonna spend a few hundred on wifi setup you mite as well spend the hundred or two hundred on some conduit and outdoor cat5 or cat6 rent a trnch digger or a few friends with shovels and do it the right way.