If you go on a presentation, you can get a discount, but why would you want to go all-inclusive? You'll be walking distance to town and there are so many good places to explore for food and beverages!
I love Grand Solmar, but the all-inclusive prices just don't make sense to me. Some of the food is great, and we always enjoy a few meals at the resort, but for the price, you'll find much better variety and quality of food off site. You have to buy an all-inclusive package for a minimum of three consecutive days, and DH and I would be sick if we tried to ingest $500/day worth of food and drinks for three straight days!
(It might be fun to try it for one day, though!) Alcohol often seems to be a deciding factor when people want to buy an all-inclusive package, but ordering the Drink of the Day and enjoying Happy Hours will keep the bar bill way down, too. There are kitchens in even the smallest units at Grand Solmar, so enjoying a simple meal or drinks on your oceanview balcony is a delight as well!
If you don't want to leave the resort, and really want to go all-inclusive, Grand Solmar usually offers a discount if you purchase it before your arrival. It's not much of a discount, though. Maybe $10-20 off per day.