Since you mentioned late spring another option might be Placecncia because you can
Dive with Whalesharks then at Gladden Spit which is about an hour ride. It's only around full moons from about April to Jyly when the Cubera spawn, Popular so prebook if you go
Plus it's a starting point for a lot of the jungle tours, Mayan ruins, cave tubing etc
My friends stayed there a dove with Splash Divers all week, They did 2 WS trips (costs extra) and saw 8 plus snorkelers on the boat saw a few more. Splash also can book your lodgings, they bundle it with diving at several price points, Their sister company books the jungle tours,
One of my friends is basically cheap so he found a cheap apt. in town - clean/a/c around $40. There's also nicer beachfront resorts a little north of town. Splash will pick you up at the airport and drop you at your resort then pick you up daily for diving.
They even used to offer a 2 day trip to the Blue Hole, the first night is at one of the Atoll resorts
Most rides to the outer reef from there are about an hour, Splash told us that limits them to 3 dives/day.
I have no personal experience with the Blue Hole but others have posted you have to go deep to get below the rim plus the sharks are often near the bottom which I believe is around 300'
I don't think it;s worth the time or effort. You can dive Blue Holes off Nasau or Andros and they're shallower and 20 minutes away, One on Andros you can drive to. Ive dove two in the Outer Islands, In both cases the dive around the hole was better than the hole itself,