NDL at 80ft on *air* is over 30 minutes...Use 32% and you get like 50 mins (I don't have tables handy, so these are estimates).
As far as gas, at 30 ft, you are at 2 ATM, at 80 ft you are at 3.5 ATM, so you are using close to twice as much gas.
That being said, most of my scallops dives (which are very few) were done closer to 60 ft than 80ft, where you have well over an hour of NDL on 32%. You'll have to calculate the gas requirements out yourself, but a large single tank should do fine, or you can dive doubles if you feel like it. Personally, I dive my doubles on anything much below 60 ft, mostly because I only have very small LP72 single tanks and no one ever died from having too much gas available.