Welcome Aboard CJ.
There are usually lots of apartments available on the west end. A lot of the hotels will give a good rate for a long term stay as well. It wouldn't hurt to contact them and get some quotes.
I recommend that you finalize something when you get there . There are too many bait and switches going on to pay in advance.
There is a wide variety of choices and prices.
As an example,
When I did an extended stay there is 2005, I had a comfortable apartment with hot water and cable for 250 a month. (I lucked out)
You may know this already, but I strongly recommend that you don't let anyone know your budget - you will have half of Negril after you if they hear those numbers.
You came to the right place - we have lots of long term visitors here and I'm sure you will get some good advice.
One more thing, lots of our folks who stayed on the West end had major water issues - another words NO WATER for an extended amount of time last winter. This is another good reason to not jump to fast giving anyone your money - you may want to stay somewhere that did not have water issues.