If it is complete with a 5x4 mixing box and masks, £300 is a fair price. Masks & boxes are few and far between and can go for silly money at times.
 The guy had it listed for £380 and no takers - Only comes with a 35N Femomask and a 67 Femobox. No timer, but it does have the transformer and a 50mm lens. It also appears to have all the dangly knobs which is good, although you might want to ask if the fine-focus on the right hand side is still there and in good order.