If you only want to spend a day in Santo Domingo you can try the trip by bus by your own.
Of course you can take the trip organisated by your tour operator, but you should expect to pay at least 55 USD per person. It's a quick visit... Not for me.
But if you prefer to go by yourself, it's posible to do it.
Well, from Punta Cana, you can take a express bus without stops. Check this link:
http://www.bocachicabeach.net/images/misc/bus_santo_domingo_punta_cana.jpg
If you don't speak spanish, feel free to email me. I suggest you take the bus at 7 AM. You will be in SD at 10 AM (more or less, it depends on SD traffic, which is quite problematic...).
You should be able to walk around Colonial Zone, stop wherever you want, have a Presidente at Calle el Conde, and also, take a taxi and perhaps visit el Faro a Colon or Los Tres Ojos (if you don't have enough time, don't worry, Colonial Zone it's worth it).
You can take the direct bus from SD to Bavaro at 4 PM (quite early, I think). So, perhaps you would prefer to take the bus to Higuey (the bus stop is in Parque Enriquillo), and I don't know exactly at what time is the last bus, but I suppose not early than 7 PM. From Higuey you can take a guagua to Punta Cana (last bus: 9.30 PM...).
Prices:
Express Bus Punta Cana-SD: 125 pesos (you should also take a taxi from your resort to the bus stop in Punta Cana, the price depends on which hotel you are).
Bus SD-Higuey: About 75 pesos.
Bus Higuey- Punta Cana: 20 pesos.
(prices per person, each trip).
Well, If you choose this option, I hope you speak a bit of spanish, ...
Don't doubt to email me if you need more info, phones or something like that, ok?
I will put in my web page photos from my last trip in SD. Check it in the next days.
(And excuseme from my mistakes in English...)
Beatriz
http://www.beatrizweb.com
"La web de la Rep?blica Dominicana de Beatriz"