This looks like a fun little project that might run near $100 assuming one needs to get all the parts. The Predator from I-Hacked essentially extends the range of an open wireless network, rebroadcasting it in a secure mode that you can hop onto. It does this with an external antenna and DD-WRT.
Does this have any uses? Well, I doubt anyone wants to cart this around on a trip, and it certainly looks suspicious in a parking lot. But it might make a decent addition to a wardriving car/truck/van setup. A few years ago this might have been a fun idea to get wireless access while around town, but these days cell phone-to-laptop Internet services and gear seem to be solving this problem. This could obviously be used to surreptitiously connect from a distance to closed wireless networks that you have cracked. Although it might be more useful to just plop the antenna on the laptop and crack/access that way as well.