I got married at Melia (as you might now they share a common area with Paradisus) and Arrecife is their official photography provider too.
They do not ask for a deposit, they take your word as a confirmation. The are gentle, ant they really care about what you want: your tastes, desires and expectations about your wedding pictures.
Then at the moment of buying, they show you several options and packages, so will find -for sure- one which fits your needs. Anyway they are always open to modify their packages if you need to add or change anything.
About paying in cash, I found it very common at the Dominican republic -no matter the kind of service you are paying for- they always give you a better discount if you pay in cash, I guess that is why they suggest you to do so..
You will really love your wedding pictures! we have received a lot of clompiments..
Share some of them with us! and happy planning!