If you weren't too fussed about 'authenticity', ie. matching numbers, there are quite a few big bikes you could ride away on for your budget. Triumph twins are usually fairly reasonable if they've had an engine swap (and I personally think a Bonneville hasn't been used properly if it hasn't been thrashed for a period during its early life), and the less sporty AMC singles and twins appear at quite reasonable prices from time to time as most people are looking out for the sporty CS & CSRs. BSA twins can be quite reasonably priced too - particularly the unit 500s.
Reliability issues are not that cut and dried as all old brit bikes are unreliable if compared to (and used like) a new Honda. However, Electronic ignition, regular maintenance and a bit of an easy life should mean you'll always get to where you need to be. Hope I haven't added to the confusion. Old Bike Mart is good for ads, and tends to have more realistic prices than somewhere like Ebay. HN