I think we paid 795 for a 52 pack of Pampers last time at La Sirena, and when I say "Pampers" I actually mean the brand, which is not necessarily what people mean over here. Usually, we buy like 32 or 38 for 595 I believe (confused about the number, since they are always different depending), also at la Sirena. Jumbo have the same prices, as far as I know. There are other brands too, of course, but we only go for Huggies and Pampers. Not sure if there are any Dominican made diapers out on the market, but if there are, I have my doubts regarding their capability to keep the little one's present contained where they should be.
Both diapers and baby wipes should be bought at Pricemart, in my opinion, since it is very hard to beat their prices (especially when it comes to wipes). You can find it on Charles Sumner close to Churchill con Kennedy. And I think there is one or two more at other places.
Prin is in Santo Domingo Este, yes. Right on the traffic hell hole Carretera Mella, next to El Cumbre (big green building) and not too far from Megacentro, which is the best landmark. If you go from Megacentro towards Charles De Gaulle, you have it on your left side. It is not too far from where we live. Want us to go there to check something out for you? We could probably find a thing or two for our little one as well, so it wouldn't be much of a sacrifice. Never been there myself, so I have no opinion about it.
El mundo de juguete and Juget?n are two other places to check out.
I can recommend Novia de Villa as well. Not saying that they only have top notch toys, few things are top notch in this country, as you probably already know (or will learn fast). But we always find nice stuff for our boy. They have one store in Megacentro, but you would want to go to the principal on Roberto Pastoriza, casi esq Lincoln, if you really want to see everything they sell.
One thing I would buy in your country before I left, is a proper infant seat for your kid to sit in when you go for a drive. You wouldn't believe how hard it was for us to find one, given that few Dominicans even know what they are, let alone care about them. There are some front facing car seats for infants, which I know lots of people use in the developed world as well, although they are in fact not very safe for small kids fragile necks. But, if you want a rear facing car seat, you will have to search and search. It took us many weeks to find one that was good enough to be used, although it could never match the quality the hold in our country (and it just cost us a tenth of the price as well, of course).
If I remember, I can check some prices for formula the next time I go to Jumbo or La Sirena, but we never used them for our kiddo so I have no idea as to what brands that can be recommended.
Anyway, PM any questions and I will see if I can answer.
Take care!