Last month, I purchased a RPB/ Powder Springs M10/9mm double stamp. At this point the market is at a high for any MAC firearms. Obviously MGs only go up in value, but the MACs are pushed into a new price bracket primarily due to Lage uppers, SABRE upper, and better stocks.
M-11s have a lot more options, but the M10/9mm is built a little beefier.
Currently, a dealer on Uzitalk is making an affordable, reliable metal magazine for the M-11 that is a great alternative to either zytel magazines or a sten magazine conversion.
As for M10/9mms, RPB industries is making original magazines for around $50 now. It is possible to convert Suomi stick magazines to work in the M-10/9mm (what I am doing), and there is the option of having the grip replace to accept cheap Uzi magazines. I was going to do this, but did not want to permanently modify the firearm.
All in all, a MAC is a better option for the "one-SMG" owner who wants the most versatility from the gun.