This is the big sidevalve banger that Ariel made forever. For a few years in the early 30's they made it as a sloper to suit the current fashion but kept making the upright version alongside it. Survival rate not impressive. First it came out during the Great Depression when selling anything was hard and secondly it shared the same cycle parts as the rest of the range so was the ideal cheap second bike cannibalised to keep the sportier ohv Ariel running.
Value depends entirely on condition and if you have to ask here that usually means the lower end of things. Incomplete and a non-runner I'd say three pints or a packet of fags plus an introduction to your girlfriends ugly mate.
Don't get me wrong, big sidevalve Ariels are terrific bikes. Mine pulled a chair and I had it for ages. Not fast but plonk along all day without fuss. Ariel made excellent bikes but their big sidevalves were the workhorses of the range, definitely not sporty.
Cheers, Bob