[cr0sh]

If you dig around on Ebay, you'll find a ton of various kinds of Model M buckling spring keyboards for fairly decent prices; usually starting at around $50 USD. You might have to do some cleaning, but that's fairly easy.

You'll also find a ton of "specialized" Model M and other IBM keyboards that were designed for certain tasks - tons of extra function keys and strange layouts.

What you have to avoid (or look for) is to make sure they aren't the "silent rubber dome" kind - there were many Model M keyboards that used cheaper (but quieter) switches. Or that might be what you want. They are still (usually) good keyboards with a lot of life left in 'em - but if you want the real sound and experience, then buckling springs are where it's at. I haven't been able to find another kind of mechanical keyboard outside the Unicomp that comes close (and the Unicomp is a identical beast - I own one and two other original Model M keyboards - they all feel the same).

There are also a lot of different kinds and makes/models of the Model M - and then you have the whole Lexmark series of Model M (and the various different IBM logo labeling).

One of my Model M keyboards is a bit unique from what I understand: It's a Lexmark, with the blue tilted IBM logo in the corner, but it has the flow-thru slots and tray under the keys. From what I understand, Lexmark supposedly didn't make the flow-thru model. I don't know if mine is a unicorn, or if the collector market is confused or what; I suspect the latter.

Oh - one other thing: Connectors. The Model M was made with a variety of cable end connectors, and is another thing you have to look out for. You may have to rewire or buy/build an adapter (and it wouldn't surprise me to find that there were also different controllers in the keyboard itself, not all being able to communicate with a regular PC).