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As GC5 mentioned neither lens is killer, the sears zoom would make a great paperweight, the 50 f1.8 isn't bad, it's pretty sharp but they're pretty much give away nowadays...but if you need a 50 f1.8 get Canon's nifty fifty, it's under $200 new and you don't need an adapter
If you're planning on shooting film the AE-1 is an easy camera to use; a no brainer. But given it's 30+ yrs old, it's light seals might be going or gone, the shutter probably has the classic Canon squeak and the mirror seals might be bad also...finding batteries for the old bodies isn't a trip to Best Buy, they'll be speshul order. Having the body serviced is possible but that ranges between $125-175; not including parts...but lenses and accessories can be found quite cheap.
I'm still shooting with my old Canon gears; A-1, T90 and lenses but it's not often anymore. As others have said the old lenses work well on m4/3 systems, the NEX bodies, etc.
I've tried a few adapters and so far only the EdMika .5mm adapter works well, but it's only for 300mm lenses and above and it's $175 (mounts to the body then any FD mount lens mounts to the body....it's easy to use) I've used Canon lenses, primes and zooms below 300mm with it, but you loose infinity focus. A 200 f4 macro that is killer will focus 1:1 and out to about 65ft for non-macro shots.
Ed has some new custom adapters that are specific for the newer FD mount; like the 50 in the craig's list picture, these require you to disassemble the lens mount and then replace it with Ed's custom brass mount...again these adapters are about $175 each. If you have some of Canon's older L glass or some of their f2 primes they make really nice conversions. Marty, an FM member is producing custom brass adapters as well.
I'd save my money if you're not gonna explore film...get used or new EF 50 f1.8 and be happy