I saw a post about a Walmart close to TTR. Is it wise to just by sunscreen there, rather then taking it with you? As weight of the sunscreen could really take a toll on the weight limitations of your luggage.
There is also little stores close by that sell it as well but be prepared to spend 10 to 20 a bottle.
I buy sunscreen in the airport once through the security gate. It's very expensive in Cancun. It might take our hand luggage over the weight limit a bit, but they don't weigh the cases again so I figure as long as it fits in the bag nobody will know. Same with insect repellent, way too much in Cancun. Other toiletries at the Walmart are what you'd expect price-wise.
A couple cans of aerosol sunscreen, or a tube or two of lotion cannot weigh that much. Bring what you need from home, and you will have exactly what you want. Our bag with sunscreen weighs nothing compared to the shoe bag. You could pay an overweight fee, and still be more economical than buying $20-30 sunscreen at the resort.