Interesting collection but I think the estimate is rather high! A diary of a FEPOW went for £360 in an auction recently (and was promptly resold on Ebay - but went for about the same amount) so £500+ may be a bit optimistic.
Well, they sold for £1400 - so that shows what I know! From the BBC: The collection was expected to reach £500 when it went up for sale in Ludlow, Shropshire, on Thursday. However, it was sold for £1,400 to an anonymous bidder, who was expected to keep the collection in Birmingham. BBC NEWS | England | West Midlands | 'I wish these air battles would stop'