Yeah, 150 quid is a bit too much I'd say. Sold mine for 60 euro at a demo party. Now that's a good price I gave, but I think you'll be able to find one for 80 euro. From your post it looks like you already found one anyway. You won't regret it if you buy it for less than 100 euro.
A lot of newer demos are made specifically for 030+, and you can easily have a 64 color AGA workbench without noticeable slowdown. Oh and you can run doom pretty smoothly if you have more than 8mb RAM for it
