Why do you say Pico Duarte is OK?
It's not as pretty as it used to be because everything was torched by a forest fire and even before that it isn't quite as pretty as say, Dominica. It's still nice though and worth the climb, but the forest is apparently almost all gone.
Would it take a day to drive and climb it?
Actually, once you are in DR, it takes most of a day to get there and to get permission and arrange guides. Most people take 3 days for the climb, but it can be done in two very long days. However, in a 2-3 day trip you will miss the best part which is the Valle de Tetero which requires an additional day.
So you need a day to travel there and get permission and arrange a guide (you have to have one by law), three days for the climb (or two very long ones, but you will have to really talk the guides into letting you do this and they
may charge you the full 3 day price-though it still is possible) and part of a day to get back to the coast. I'd plan on 5 days for Duarte alone once you land in DR, though you might be able to shave a day off if you are really in a rush. Add another day to see the Valle de Tetero if at all possible.
You could possible do Duarte round trip from New York in six days, but forget about seeing anything else like the beaches, rafting, etc. If your GF is OK with you leaving her for five days for Duarte, there should be plenty for her to do elsewhere.
Also, as the SP page says, I'd recommend taking a tent. The huts can have serious rat problems. Either way, don't forget sleeping bags, etc. unless you go with a really high end company. Only the high end companies will have sleeping bags for rent. Iguana Mama is probably the most high end company, but we used a cheaper fly by night operator and brought all our own food, stoves, etc.
http://www.iguanamama.com/pico-duarte-a ... -dominicanPrice depends on how much services you want. If you take all your own camping gear and food and use a local guide (most of which won't have an email address) it will work out to be cheaper. If you don't want to haul all your camping gear to the Caribbean, there are guiding services that will do that for you, though you still want your own sleeping bag.