Hi Michael..Check out e bay.. 230756388470 ..They are still well behind ww2 bikes in price. I think a couple of thousand will buy you a good runner..and I've seen them for less.
I ran one for a few years and they are basically a good bike. Points to consider are they are very low geared as they are fitted with a 'trials' type gearbox. Many of them have had this replaced so if you want an original one that is a question to ask when looking. With the original gearing the revs are uncomfortably high at normal cruising speeds.
They also had a 20" front wheel so tyre choices are strictly limited. I changed mine to a 21" and used readily available block tread trials tyres.
The original carb was an odd ball (a Zenith if memory serves)..again I changed mine to a Mk1 Amal and put the original on the shelf. Again, many have had the carb replaced.
The full chain enclosure, bag carriers and bags are also VERY hard to find.
On the plus side they are light, have a good frame and forks, an external oil filter as standard and a low compression top end on a pretty good bottom end.
I quite enjoyed mine and the chap I sold it to about 20 years ago still has it so I guess he liked it as well...
Jon Small bought a very nice one last year and if he sees thispost I'm sure he will comment..Despite being the 'poor relative' of the ww2 bikes (along with the TRW Triumph) both bikes have a growing following and prices are on the up...I believe there is an owners club, forum or similar so it might be worth a Google search..also try Milweb..they seem to turn up on there periodically....Ian
email (option): ian@wright52.plus.com
the army taught me to ride on one in the early 70's...great stuff.
email (option): chris.astinbarker@btinternet.com
ah cris b we were young then any ride on a motorcycle was wondeful but even then i liked the M20 
email (option): roger.beck@node6.com