This is a much revisited topic.
I'm not sure why people are so dismissive of Spink's prices. Nobody has a monpoly on accurate numbers. Not all things are overpriced in Spink. The further back in time you go the better they resemble the market.
Using ebay listings could be interesting. 50p washers for 100 quid on ebay - not an uncommon occurrence and something guaranteed to skew the data. A 50 pound item going off at 3 in the morning may well sell at 99p - again skewing the data. Auction houses have as much variation as eBay too, with the sale presentation and contents having far more influence than the reference volume prices.