Yeah those quotes are a little expensive {in my opinion} for only three nights. However considering the locations, that may be the going rate. We originally looked at Punta Cana and Jamaica but due to nigher rates, we switched to Mexico. We were quoted something similar for a resort in Punta Cana for three nights. Our guests are paying ~$850 for 4 nights and airfare {booked separately} to attend our wedding.
If your heart is set on Punta Cana and Jamaica reach out to other TAs who specialize in those areas. Some have a "relationship" with different resorts which could result in lower rates.