If you were to sell it here in Australia I'd think you probably wouldn't get more than AU$1,000 for it as is. BSA side-valves have never really been hugely valuable because of the commonality and undesirability - but having said that, restoration projects like this 'barn-find' are getting scarcer and more sought-after. The fact there is no carburettor, electrics or exhaust pipe are not in your favour either. It may or may not surprise you to learn that the most valuable thing on your particular bike is the girder forks!