my friend is looking at a valmet m76 5.56 assault rifle in good condition pre ban, how much would this gun be worth?

Probably around 1800-2000'ish.

search on gunbroker and sturmgewehr.  Remember, the 76 only works with real Valmet 76 mags which are HARD to find.  Many times I'll see a Valmet 76 selling with one original 12 round mag and a bunch of bullshit 223 AK mags or modded Galil mags.  Maybe they work but I'd stick with the 76 real mags.

Valmet 76 is really a collector's piece now.  Can't find any parts for that sucker.

Valmet 76s are going for $1200-1800. They work excellent with modified Bulgarian .223 mags. There are a few parts available on Gunbroker, or on Valmet.org. Original magazines are easy to find, they are just expensive. Old aftermarket mags from MCP or LIQ come up occasionally & they work very well.

valmet 76s run anywhere from 1000 to 2000 just depends on how lucky you get or how much your willing to pay for one,  original valmet mags run 100+ they dont get any cheaper , the other options are german weiger mags , bulgarian poly mags, or cheap 223 ak pro mags i did two pro mags before started hacking on on 30$ weiger mags  , DO NOT USE GALIL MAGS IN A VALMET the feed angle is wrong and you can get a catastrophic failure from doing so