Colombia. EASILY.
Specifically Cartagena. I mentioned this before and I'll say it again, you're talking about the convergence of Colombia and Venezuela, two countries who have been raking it up in beauty competitions. Cartagena may be more "expensive" because that is where wealthy Colombians go and therefore the ladies follow, but we're talking about a line of beauty queens for less than $.
It's also the safer of options. Whether you're meeting a gal in old town (centro), the gentrified getsemani or either of the condo coasts to the north or south (avoid the actual beaches), you're going to some wonderful and somewhat upscale places in Latin American standards. Don't want to pay? There are matches everywhere if you learn a basic salsa.
After that, I'd say Bogota and then Cali.
After that—and they're not very close—I'd rank DR and PR after that. Mexico is a mixed bag.
Absolutely no to Costa Rica, Guatemala and Ecuador. Not that they lack beautiful women, but a lot harder to sort through.