Can anyone tell me how much the postcards are in the gift shop at CSA and if they have a good variety?

Rather than do a traditional guest book, for our CSA wedding, we plan to provide each guest with 2 postcards in their welcome bags, both stamped. One will be addressed to us and the other will be blank to do with as they please. I've read that stamps can be bought at the gift shop with cash for a little over a dollar each. I can get some gerneric Jamaica post cards on Zazzle for about a dollar each before leaving home, but I'd really prefer to buy them there as long as I won't be paying twice as much at the gift shop.

If they are more expensive, is there any place close to the resort that has them for a good price or is it worth going on the shopping tour from the resort just to pick up the postcards?