When I see the prices on some FD and FL lenses, I debate my decision - made years ago - to go with Nikon (since Nikon F-mount lenses are usable on their DSLR cameras, prices are noticeably higher than Canon MF lenses). As a landscape photographer, I am very interested in wides, and I have a friend who considers the Canon FD 20mm a superb lens - but at $300+, this is well outside your price point. Still, an ultrawide is one way to broaden your horizons!
PS: GAS = Gear Acquisition Syndrome. We all have it to some degree.