I don't follow values much but seems to me that a dog that the seller thinks has great potential will go for $1,500 - 2,500.
Something with actual potential is probably 2,500 - 4,500
A bike with rebuilt motor and chassis but not necessarily restored to 100% original or 100 point museum quality up to say 6,000 - 8,000
"Over restored" say $8,500 - $12,500. I would expect a perfect resto to go for at least that much if it looks exactly like a new bike fresh off the showroom floor because it would cost that much in parts and services to build one with perfect chrome, wiring loom with the correct connectors and wrapping and so on.
But those are just my guesses. Others will surely weigh in with their own experiences and expectations.
I have done a couple of restorations with fully rebuilt motors, fresh paint on the chassis and all bolts replated or replaced, & fitted with either stock rebuilt spoke wheels or GS750 wheels and stock exhausts. The last one I finished in the middle of winter and did not have a chance to ride it and I still wake up wondering what bolt was not tight or was missing or what setting was wrong. I am much happier if I can ride a few miles and trouble shoot them and work out the bugs. After they run perfectly my work is done and I like them to go to a new home.
I have another L (74) in the shop now with GS wheels with new bearings and fresh rubber, GS swingarm, fresh crank, rebored with Wiseco pistons, remanufactured water pump, All replated stock S head bolts and it will be sold with a modern regulator, rebuilt switches and wiring loom stock rebuilt carbs with stock airbox, rebuilt master cylinder, calipers, new brake lines and a Jemco 3 into 1 exhaust and Hyabusa rubber mounted rearsets with adapter brackets that mean no modifications were made to the frame. It will also have an Accent electronic ignition. Or points if the buyer prefers. The buyer can also take away a pair of stock wheels and foot pegs if he/she wants to make it stock again.
I was building it as a cafe racer and tried a few seats but none looked right so I am rebuilding a stock seat. Seat pan has been panel beaten straight and blasted and powder coated and will get a new seat cover too. That list is just to give you an idea of what goes into building a bike. As you can imagine, that lot adds up and includes hundreds of hours of work and machine shop services. This is my 4th GT750 and now I'm down to only two customs to build plus a race bike and a few other makes. Plus the other pair that someone is trying to sell me.
I do have the core of a B in the shop but I shudder to think what that would cost to rebuild to 100% stock.
I don't do "Restorations" if I can avoid it because buyers expectations on chrome finish and bolts and so on can be all over the map. For example a really smooth chrome finish will look great to one buyer and totally over restored to another. There are some really great GT750s out there. I think that Ian Sandy may have one or more for sale and he does them closer to stock than I do.
Good luck in your search.