Back when the options for gTLD were .com, .net, and .org, .net peaked at about 1/3rd of a .com's value. When the new gTLD came around .net drop down to 1/10th, now it's roughly down at 1/100th. But even that is very hit or miss, because people looking for a .com are unlikely to settle for the .net, despite the .net being the second most valuable gTLD.
Certain big ccTLD (.ca, .cn, .de, etc.) can be worth roughly a 1/10th of a .com still, but it's very circumstantial.
777.com = $X,XXX,XXX
777.co = $X,XXX
777.io = $X,XXX
777.gg = $X,XXX
Note that numeric domains are mainly used in China were .com, .cn, and .net are preferred.
hey.com = $X,XXX,XXX
hey.co = $X,XXX
hey.io = $X,XXX
hey.gg = $XXX
Similarly these would appeal more to Western users.
Of course, it would be difficult to find a buyer that would pay this much for these domains. Because the .com:s are expensive, and the other extensions aren't particularly popular.