how much will it cost to fix a blown head gasket on a 1994 nissan altima ?

Call around in your area for estimates. Knowing the price where I live won't help your much.

how severe was the melt down? were you able to stop right away? My altima sprung a leak at an impossible to find, near the startermotor moulded rubber piece that Jose the mechanic had to improvise to mend, perhaps just the head gasket isn't the only problem under the circus tent, is what I'm suggesting...also if you weren't able to stop right away and was smelling a burning smell because ALL the coolant burned off, that's a more expensive can of worms to open~ as piston pins get loose, cylinder heads will warp, bolts will stretch etc..

Just ran hot and shut it off and head was cracked