Geo -- I, too, have been a bit of a bike geek for most of my life. I have a lovely Italian steel frame, all Campy bike I built up myself -- it's a sweet ride. But, I blew out my shoulder swimming and it just hurts to much to ride my Italian steed. (Although I do air up her tires from time to time and take her out for short rides!).
I highly recommend you look at a short wheelbase recumbent. Yes, they are a little chunk of change, but you can't beat them for a comfortable ride and the short wheel base bikes are nimble (and fast!) and such fun to ride. If you are concerned about your back -- there is no better solution. Plus, it is fun to see the teenagers on skateboards stop and stare as you ride by "dude, what an awesome bike"! There are a lot of choices when it comes to recumbents these days, but after literally years of research, I settled on a Bacchetta Giro20 -- and I love it! http://www.bacchettabikes.com
. If you go to the forum on the Bacchetta site there is a "for sale" section, too. Also, look around on Craigs List and your local sites. It shouldn't be too hard to find a good used bike, at a reduced price from a new bike. Also, if you aren't near a bike shop, Bacchetta ships bikes, ready to ride out of the box -- they are a small company with can't be beat customer service.
I love mine! Good luck and welcome back to the road!