PDP model line / rarity?

<I was just wondering on the rarity of DEC's PDPx machines - I gather <that '11s are still pretty common (relatively!), but what about earlier <machines in the line? PDP = Programmed Data Processor. It was a ploy to tame down the idea of large, expensive and complex computers. The PDP-8E/F/M/A series was quite popular swith sales in the many tens of thousands. There are many of these in service as machine tool controllers and other uses. PDP-11 series was even more prolific. Rare machines are the PDP-1 (few left), PDP-5 the forunner to the 8, and 10s. The total sales for the PDP-1/4/5/6/7/9/10/12/15 combined was under 5000 units. Generally the 18 and 36bit machines are tough to find and if found represent a bit of work to run. Allison