The Yam YZ250N was a great bike in '85; it had a lot more top-end but would still rip from low-down.
I think in the late 90's the government made all tax (GST) 10%, that pulled the price if bikes down a bit.
I remember a few years back new bikes were over $10K but they have come back down a bit now.
I just swapped my 2010 YZ250 2-stroke for a 2011 RMZ450, I'd swear neither of them handled or performed as good as my '82 RM250Z (except brakes).
If you could still get a brand new 20 year old bike, it would be just as good as todays bikes I reckon.