First you need to decide where you want to travel to...you maybe able to get under the 2k range but pay more for airfare getting there.
So you need to determine destination first.
But staying close to home (US and Caribbean) in addition to some of the suggestions already posted.....
There is the S/Y Juliet out of Miami
There is also the M/V Spree (somewhere in Florida - Gulf of Mexico itineraries)
You’ve already been introduced to Explorer Ventures - They run Caribbean itineraries under 2k
The Gulfstream Eagle ran out of West Palm Beach, Fl...but I haven’t heard anything from them lately.
Then there is Thailand...which is liveaboard heaven. Of course the Maldives, Indonesia, Solomon Islands, etc..etc..etc..
There is also the Red Sea which has a lot of liveaboards as well.
I’d give the Juliet a REAL GOOD look. You’ll love sailing and diving with them and the price is right.