I would reiterate pretty much what others have said already. If you decide to send flowers online, you're looking at approx. $50-75 USD for the smallest arrangement. Mother's Day in RD is this coming Sunday, May 30th.
I have bought rose bouquets in Santiago, Cabarete (well, a bit further east) and Sosua. I have paid approx. RD$500-700 (approx. $10-15USD) for a huge arrangement, and that was probably a gringo price.
Take advice from the board, if you have a contact there, send them the money and have them buy it there. Give them a $20 USD commission for their services, and you still break out way on top. Plus, you have the personal touch of someone overseeing the flowers for you.
Best of luck.