I've use this answer before but think you can benefit from it as well:
Its very easy to find good beaches in PR, you're actually very close to the water wherever you go. Good surf spots are in Rincon but Luquillo is probably closer to where you'll stay for beaches. Fajardo has good beaches & the best local beach food in beach kiosks (kiosko o kiosquito). The best beaches in PR are in Culebra, its a minor outlying island right off the coast or PR, you can catch a ferry to go there, its really worth it.
The water is clean & drinkable everywhere. Stay away from stupid people that might look dangerous if you venture into an unknown dark alley (common sense really). Camuy is a bit of a drive from the metro area (San Juan) and it has beautiful caverns that are quite touristy... stalactites & stalagmites, etc, you can probably find some pretty good food down that way as well.
Prices in PR used to be cheaper than most states but very recently (within the last 2 or 3 years) they've applied sales taxes to everything. So while some prices are probably cheaper than most states its not like going into Mexico or a country with its own currency thats worth less than the dollar. You use $US currency there.
You do not need a passport, its like flying to NY or FL.. Be prepared for humid heat & lots of sun. I can recommend Culebra, Fajardo & Luquillo for beaches, Fajardo for beach foods, Guavate absolutely has the best local delicacies (whole roasted pork over a pit kind of thing) and has been featured in the Food Network (Anthony Bourdain ate there). Plaza las Americas is the best mall to go to if you find yourself wanting to go to the movies or need to shop for something.
Spending your entire stay in San Juan or the metro area is a good way to not experience the caribbean island part of PR, so do try to see SOME part of the island while your there other than your hotel resort.
Hope this helped, email me if you need any specifics or directions and above all HAVE FUN!