Linksys (and no doubt other manufacturers) have N access points. Check the Linksys site. Pricing seems to be in the $160-180 range. The G model I recommended is about $80. It doesn't have power over ethernet. Only you know your house. If you can power the WAP from the wall, then you don't need POE. It's cool, but you don't need it.
If you can get a wireless N WAP up high right next to a window ... maybe you can get a decent signal on your Mac at the other house. Certainly it's possible, but it's pushing it.
The issue for you is to decide whether you want to have a classic wireless setup (one station, many devices connecting) and hope that you can manage to extend the signal over a larger area, or whether you want to have two areas that are connected by a wireless link.
If you go the wireless link route, then you really need 2 equally powerful and identically configured WAPs, one at each end of the link. As for using just one WAP/hi gain antenna, I read an analogy somewhere -- let's say you can throw the ball 300' and I can throw it 200', and we go play catch. I go out 300', catch the ball you threw, and...oops. I can't get it back to you. Not a good game. Both sides of the wireless pathway need approximately the same capabilities. Remember, the signal is passing both ways, not just one way.
If you go the "extend the range of a single station" then you only need one router or one router and one WAP, to get the WAP closer to your remote location.
It's your choice, obviously.
Two G WAPs -- about $160
Cables, etc. -- maybe $60-$100 depending on length (those RF cables can be expensive)
Antennas -- 2 @ $70 = $140
Two Linksys N WAPs, no high gain antennas, about the same. If you go that route, you need to make certain that the N WAPs can be put into "bridge" mode. If not, then having two is a waste.
So you'll have to spend about $400, maybe less, maybe more, shipping, and so on.
If you're a tinkerer or know people who are good with sheet metal and general fooling around with tools and materials, then you could get 2 of the G WAPs and, like the guy with the Pringles can antenna, start messing with reflectors. The G units have external antennas so you have a lot of options. You might find that you can make something yourself that's good enough for the link.
I don't minimize the money issue. But, as another poster pointed out, the configuration I recommended to you is the standard one, used widely and is, as the saying goes, "known to work."
