I used to buy/sell/trade a boat load of powder burners. Now that I look closely at the 777s and after owning a rebuilt 717, I would say that a 95+ 777 without original box and all inclusions would be worth $400 if it was rebuilt with a good exhaust valve. Probably add $100 for a good condition complete box (papers, pellets, tools, lube, patches and rod) with a good condition Daisy shipping box. I suspect the only difference in complete takedown between a 777 and 747/717 is that on the 777 you must raise up the metal rear sight all the way till it will flip forward and loosen the screw that resides inside till the clam shell comes apart. After that it is all the same.
I'm going to keep both of these 777s and order an Ambi grip for one. I can shoot either LH or RH and that will allow me to shoot 2 at once or shoot LH or if a LH shooter wants to shoot with me or if a righty wants to shoot informally.