There are a couple of ways. First you can get a Linksys router and modify it to add a serial port. There is a thread in their RC forum that has a modified firmware to load that will enable the serial port. This is the cheapest option and can be done for under $100 if you can solder. The next option is to buy a serial network adapter and then buy a wireless gaming adapter to plug into it. Basically the serial network adapter adds the network port to the ACjr. If you buy the stuff used off ebay you should be able to do it for around $100 to $125. The last option is to buy a wireless serial port adapter. These are used to make retail items such as older cash registers wireless. Cheapest new one I've seen is around $160. Used ones show up occasionally on ebay but every time I've bid on one they get too high for me.
Check out the forum on RC. ChrisRush has a thread he started there a while back that has a lot of info.
