Nothing in Hawaii is inexpensive...on any island. Personally my two choices would be Maui and Kona. You already want to see the volcano and have to be on Maui.
Dives on either island are expensive. In Lahaina Extended Horizons does 2-tanks to Lanai for $149 - $139 for a shallower 2-tank afternoon dive off West Maui. I think Lahaina Divers is slightly less but their website is down. There's a lot of shore diving in West Maui also. Lahaina Divers or Maui Dive Shop in Kahana (near Kaanapali) both rent tanks/wgts. etc.
Scuba Shore Diving Site Listing for: Maui, Hawaiian Islands - one good dive in downtown Lahaina not on this list is Mala Pier - Lahaina Divers does it off their boat at night also - much easier entry than the legal entry which requires navigating coral heads at night.
You'll want to do at least one boat dive out to Lanai or Molokini if it works in your schedule. Either the Cathedrals at Lanai or Molokini Crater are the signature Maui dives. The two boat operators are Lahaina Divers or Extended Horizons - Maui Dive Shop keeps their boat in Ma'alea - about 1/2 hr. south of Lahaina. Both operators leave around 7-7:30 and are back by noon.
To save money on Maui, rent a condo and cook some. November is before the Humpbacks show up so although it's "High Season" there's deals. Try one of the huge condos complexes in Ka'anapali - near everything, (including Lahaina) it might be more affordable. Up around Napili Bay also - smaller, older beachfront condos - 15mins. drive to Lahaina.
VRBO® is Vacation Rentals By Owner is your starting place.
Or options in Lahaina - Lahaina Shores, Aina Nalu, the Best Western Pioneer Inn... Rent a car, the flights below are predicated on landing at Kahului - on the eastern side of Maui. It's a 30-40 minute drive to Lahaina from there. Cabs are also pricey on Maui. Rent the car before you get there also - it can be a big $$ difference.
I might do 3-4 days on Kona - do the Manta Night Dive, some day dives. To keep costs down there's at least a dozen shore dives also. Most of the shops in the Kona area rent tanks. Condos just south of Kona can be well under $100/nt - again check vrbo.com. We like Kona Diving Company and Jacks Diving Locker also gets a lot of positive comments. Both are in Kona but all the Kona operators keep their boats at Honokohau(sp) harbor just north of Kona so pick one you like. Big Island is also mentioned often. Jacks has a Manta Night Dive video on their website to see what that's about or there's dozens on Youtube.
Volcanoes National Park is at elevation so you need to have 18hrs. after your last dive before the drive up there. We had a red-eye flight back so planned to drive there that morning. You also can't fly between Maui and Kona without following no-fly rules since they pressurize the flights but there's a bunch of stuff to do on Maui.
To take advantage of the shore diving you'd want a car - not cheap either but a lot less expensive if you book in advance. It really is the "Big" Island so everything is a drive. Several hours to Volcanoes Natl' Park - all day to Hilo and back.
[-]Go Airlines,[/-] Hawaiian Airlines, Island Air or Mokolule are inter-island flight options. If your dive gear fits in a conventional suitcase, there is no extra charge to fly it besides whatever their per checked bag charge is.
I just ran a quick comparison - it is
Substantially cheaper for you to fly to Maui first, then Kona, then home. Here's an example for the first 10 days in Nov.
Oops - I cut the price off but it was $1421pp. This price allows you to keep moving back to Nashville non-stop with short layovers. If you want to overnight somewhere along the way, the best price was $1215pp.
Routing thru Kona first the best price I could come up with without an overnight layover was $2715. The cheapest with an overnight layover on the return was $2400. The routing was worse, to get from Kona to Maui you had to go thru Honolulu. You're fighting the clock so that last flight home is long and connections either way.
I use this website - it's the same information found on Google Flights since Google owns it. Also Kayak.com and multiple others. You just can't book anything on the Matrix site.
Matrix - ITA Software
Have a good trip. Hawaii diving is substantially different than the Caribbean since the substrate is volcanic.