I'd highly recommend Fiji, and some time aboard Naia. It a live aboard boat that has been operating in Fiji for decades. They have built relationships with villages in the areas where they cruise. So real local interaction happens during the trips.
But it's the diving that is the big draw.
Water temp is cool to me. marine life is spectacular, colorful soft corals, brilliant tropical fish.
Giant clams keeping a lookout for intrusion into there local. And snapping closed.
Many top pro photogs have been aboard, so there are great videos and pics to check out.
May not fit the budget range you mention, but the diving is top notch.
Life aboard is great, excellent food, friendly mostly Fijian crew.
Time in Fiji will be memorable!
https://www.scubadiveasia.com/scuba-diving-vacations/fiji/liveaboards/naia/?gclid=COjvvs-d5c8CFQ9xfgodQeYOZw
Cheers Richard