Like you say Mark Bill Bush was £150 few years ago and with the amount of copies about now should be, in theory cheaper and available to many more collectors as it is far more common these days...in theory! As with many aspects of this collecting scene demand is pushing the price sky high for items that really don't warrant such prices. Bill Bush and the Cashmeres prime examples, both often fetching a four figure amount ($) :o
Bobby Kline, Johnnie MAe Matthews, Tangeers are other recent examples as is the Hyperions, was watching two copies on the same e-bay page (highest priced) earlier in the week, one went for over a $1000 dollars for a record that shouldn't be anymore than £400 IMO, probably less with the number of copies around. Again demand pushing up the price.
Doubt very much I would go out and buy these records if I had the money. To me, as good as they may or may not be, they have had their day and time they had a rest, have been hearing them for 15 years and more now. Would much sooner find a semi-known or unknown, whatever the price, preferably cheap, than buy over priced indemand records.
Like I said if records were priced by it's availability and rarity then more of these records would be available to the average collector.
Each to their own though