I have a couple of BSA's gathering dust too. Been collecting parts for YEARS to resurrect whichever I can over the coming winters. The Bonnevilles keep one busy chasing minor repairs and hunting down the correct bits (speedos are costing more than I paid for the ENTIRE BIKE).
Used to be that you could pick up a Bonnie, Trophy, Tiger, Commando, Atlas, Lightning or a Thunderbolt for under a grand running. Last bargain I saw was a Dommie-engined chopper...Purple Paisley, a girder that was at least 7 feet long and a white button-tufted seat. Hadn't seen the road since 1970.....$500.00.
I know of a Fastback and a Hi-Rider tucked away but passed-up a Rocket3 a year ago for $2.5k....the woman at home would have stabbed me in my sleep.