Meaty, there is a wealth of information over at uzitalk in the mac forums. There are some really knowlegable folks over there.
I'll try to answer your questions the best I can.
I bought an M10/9 from an estate sale last year for $2800 including the transfer tax.
Though note that I have spent more on the Lage upper, Practical Solutions 22 upper, and basically just personalizing it the way I want it.
With the economy the way it is, now is a buyers market for machineguns.
As for the issues noted above with the old original buffers, they're just a piece of rubber and can be replaced for about 2 bucks each and there are lots and lots of aftermarket accessories for them.
Here are a few key places of interest:
LAGE Mfg. Products: M-11/9 M-11 M-10 M-10/9 M-10/45 Cobray SWD Powder Springs
US Machinegun.com : Machine gun accessories of all types
Practical Solutions (Powered by CubeCart)
Here is a link to the dealers website who handled the first part of the transfer to me and he has several NIB macs' to choose from for not much more than $3000. D&D Guns - NIB MAC 10'9's
Here is a couple of pics of mine:
With the Lage Slowfire upper before I refinished it
After I refinished it with Moly/Teflon
I also modified some old Suomi 36 round mags to work in it for a couple of reasons.
#1. Their feedlips don't wear like the old zytel 32 rounders
#2 They are made of a very high quality metal
#3. They are doublestack mags and much easier to load
And some 50 round monster mags with a 36 rounder in there for comparison
And my new toy for it, a Practical Solutions 22LR conversion kit
And just for giggles, here's all 3 of my uppers
For what it's worth, Mac's with Lage uppers have been giving the MP5 guys some serious competition lately. Most recently was the last Knob Creek subgun match (where a Mac took first
And I suppose you may want to watch some video's so you can see some of the differences the aftermarket uppers make:
Suppressed Mac 10/9 with a Lage slowfire upper
And with the Practical Solutions 22 kit for when you feel like shooting a bullet hose economically