Even though SJU is part of the US, most airlines treat it as an "international" destination, however there is no customs and immigration to go through. You can actually purchase goods on the duty free shops on your way back. As for price, it is a bit early. I myself travel a lot to SJU, but from Chicago. Typical price for me is around $350 or so. Here is my take, if you feel comfortable, buy it now, what if you wait until latter, the price may go down, but you have other financials obligation. There are some websites that can give an idea on the average ticket price, I think it was one of the online travel portals.