Best place, way to tropical vacation on the cheap?

I’d like to take my girlfriend on a trip to somewhere nice over our spring break, I had either Cancun or DR in mind, preferably an all inclusive type deal, for 3 nights or so. We have perused Groupon deals for trips like that and found a couple relatively cheap travel package options. I was wondering from you guys personal experience, etc. what are the best ways to as cheaply as possible put together a nice vacation of the sort? Any help is appreciated