"Fair Price" is a very subjective thing...
What may be a fair price to you may not be to someone else. If both seller and buyer are satisfied, you pretty much have a fair price...don't you???
But, if one participant in the deal has the benefit of more or better information concerning the product or market, it sort of tips the scale a bit.
I bought my 124G about two years ago for about $90.00 US. I was satisfied and so was the seller. I've seen them selling for as high as $150.00 or so; but I'd never pay it...I once had the chance to pick up a D for $20.00, but didn't have the cash on me at the time...the seller was even going to throw in about ten rolls of 120 film...<sigh>...
Just my opinion, but if you got a Mat in very good to excellent condition for less than $100., you've probably done okay...under $70.00 and you've done well....