The really cheap solution is something like an Intel Anypoint (or whatever we are calling it) which overlays the phone system. These are cheap and should solve the problem with about 10Mb of bandwidth and virtually no latency hit.
The moderately cheap solution is a 1.6Mb wireless system like the Acer Aviator, Warplink or the Intel solutions. Bear in mind that you will see a fairly substantial bandwidth hit if they aren't right next to each other. I don't recommend this since I've heard a lot of people complain that the bandwidth is simply awful if there is more than one wall in the way.
The expensive but preferred wireless solution is 11Mb/s and uses the 802.11b standard. The SMC EZ Connect 11Mb Access Point ($250) and PCI cards ($170) are a pretty good solution. Or the D-Link or Linksys solutions... they are all based on the same technology so they are approx. the same. See
this page at MWave.Com for examples.
I picked up an IBM 802.11b 11Mb Wireless Access Point on E*bay for $220 last week and got it working last night. The cards I'm using are Lucent/Avaya Silver (64-bit encryption) PC Cards and I bought them for $130 ea. (yeah, I got a good deal - this setup should have run somewhere around $1400 retail).
My first impressions are pretty similar to jcastle. Real-life bandwidth is substantially less than the advertised amount when you throw a couple of walls in the way, so get something much faster than you think you will need (for my cable modem I wanted at least 2Mb out, so a 1.6Mb card would have been far too slow). Latency seems neglible. I walked down the street carrying my laptop (yeah I looked a little silly, but it was night...) and figure that the range with two walls in the way was about 400-500ft. I wasn't tracking the bandwidth as I pushed the range, but I'll give this a try when I get the chance.
Personally I'd recommend one of the phoneline solutions. It will get you the most bandwidth for the least buck. The wireless solutions are only really cool if you have a laptop.