I don't see any support for the WRTU54G @ dd-wrt.
A wireless ethernet bridge doesn't HAVE to be expensive if you know what to look for and have some patience for a deal. Right now you can get the ASUS WL-330gE travel router for $15 (after rebate). Makes a great client bridge. You can even plug it into a USB port for power, no AC adapter necessary (although it does come w/ AC adapter if you need it). It can also be configured for repeater bridge or AP. And it supports dd-wrt! (something I strongly recommend over the stock firmware). It's almost impossible to brick since it uses a special recovery mode for firmware upgrades.
http://www.mwave.com/mwave/SKUSear [...] ia=BA24255
I personally own three of these devices, each using dd-wrt, two configured for client bridge, another as a repeater bridge. They all work great. In fact, one of them I received on a Newegg deal for ~$7 (after rebate) back around the beginning of the year.
Other similar deals come around from time to time. As I said, you just need to know what and when to buy.