Well, I have thought of buying one that way. Buy an old one and bring it back to life. I might be able to afford that if I stretched a bit.
I also liked the Yamaha 650 Special (vertical twin). They seemed like a refined and reliable Triumph Bonneville.
They were electric start and sounded great. That would also be a good bike to either restore or customize.
You can find parts on forums, ebay or places like Craigs. Plus, there are always swap meets.