Get an older Linksys Wireless G Router and use DD-WRT to flash the router as a repeater. Put the repeater next to a window in the shop that is close to the house. Your main Wireless router may need to be moved so it is closer to the shop. I would not use the Powerline adapters, since I doubt they will work all that well with your setup.
Dave
My router is already as close to the shop as it can possible get without being outside and my shop does not have any windows! The 50 yards is direct from the router to the closest part of my shop where I need the computer.
I do have a conduit in the ground from planning ahead when I built the shop! I beleive there is already a cat 5 cable in there too. I just don't know how to get from my wireless router to a cat 5 cable, then back to wirless in the shop so I don't have to be stuck in one spot. Since I can already recieve some signal out there, I figured that booting it somethow was the easiet thing to mess with.
Heck, I even have my whole house audio system routed out there! I had an extra "zone" so we ran the proper wiring for it and I have 4 speakers set up with a keypad to control volume and 6 different audio sources!
If you already have a cat 5 cable in the conduit then you should have an exposed end on each end of the conduit, I'm assuming, one in the house and another in the shop. All you have to do is plug the house end of the cat 5 in the back of the Westel and then you could go direct eithernet into the laptop, or set up a access point router in the shop and do wireless....doesn't seem to be that difficult. This is exactly what I'm doing with my set up. Heck my whole neighborhood was getting free wifi until I secured the thing up.
If you don't have your Westel manual, go to:
www.westell.com/content/products/pdf/030_300444A.pdf
Turn to page 9, section 5.2 and look at the picture of the back of your modum/router. You will see 4 ethernet connections. Plug the cat 5 cable into one of those and you're in like Flynn.
I have a Belkin Access Point, but you can get d-link, netgear, cisco etc access points via e-bay or your local Staples/Best Buy etc for anywhere from $25 to $450 depending on what you want, but the less expensive ones will do just fine for your application.
Hope that helps.
Rick (mtgrizzly52)