Well, my dive gear is in route to Florida w/ K-valve, otherwise I'd consider giving it a shot. If it's not recovered by the 20th, I still might. I'd expect $100 per hour plus boat arrangements, find it or not. Otherwise, it's a fun dive and any recovered items could then be sold back...
I'm really curious about the GPS coords. IMHO, the part of the lake is big factor from a difficulty / safety factor. 80’ means it’s not likely in the river channel (around 111’ right now I suspect), which is good b/c it probably hasn’t sunk into the silt beyond sight, but also means it could be on a slope or wooded part of Travis, especially if near shore (not sometimes island). I’m not a fan of dropping vertically into trees w/ zero vis.
Last vis reports I’ve seen are pretty bad deep, especially if dropping straight vertical, which is the most practical way I can think of to hit a GPS coord on the bottom. If it’s close to sometimes island, chances are great that there are no trees, as most of the middle of the lake was cleared out before the lake was filled.
If that’s the case (no trees), a quick descent on the coord after checking depth to avoid smacking the bottom would be no problem. Then tie off a reel (assuming you can find anything to tie off on) and run a circular search pattern. With two divers working out 10' per lap, you could probably cover a 200' diameter circle before hitting deco. More w/ some visibility...
Just my thoughts… location on the lake would be my biggest concern. Trees would change the entire game plan and personally I wouldn't attempt it.