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There's a Buy-it-now M42 bellows on ebay right now for $15 delivered!
Close Up Bellows for Pentax Screw Mount 35mm SLR Camera - eBay (item 260519327702 end time Jan-05-10 12:03:18 PST)
I'd buy it if I didn't already have one. It plus a $15 adapter + an m42 lens would be a good start for high mag macros.
Dave in Iowa