$50 a night at the tail end of the high season might be a little tough (high season/high prices ends April 15ish). Call the Xtabi and see what they can do with your budget if you pay in cash (everyone likes cash). If I'm not mistaken they have AC units in the rooms next to their pool. They also offer some of the best snorkel diving on the cliffs (reefs and such) plus their caves are cool to explore. Their food/drink prices SUCK but there are plenty of good cheap places to eat and drink within a 5-10 minute walk from them. Miyard (open 24/7) is a cool place to chill and Delroy the owner also rents room, e-mail him for prices or better yet call him. Sips & Bites, 3 Dives, and any of the Rasta roadside stands will also help with keeping your costs down.
The mango should be in season when you go along with dozens of other fruits that all taste great but some of them look weird-----TRY ALL OF THEM! Ask your hotel workers when the fruit/produce guy comes around or the workers might be willing to pick you some.
Almost forgot, The Samsara is on the cliffs next to the Xtabi and their sister resort is down on the beach. The offer free shuttles back and forth that will save you about $5.00 in route taxis/$15 in regular taxis or the 30 or so minute walk. Not sure if paying their higher prices will offset the free rides or not but they do have specials all over the internet.
For transfers from the airport to Negril check out
http://www.clivestransportservicejamaica.com/ his "shared rides' are $20pp each way but generally you will be the only people on the bus.