I own a Whaler and tell you to get the kayak. Why used, I bought a new OK Scupper Pro for about 750. The kayak will cost nothing to own and store. It requires no fuel, no trailer and can be launched right from the shore and zip you effortlessly to your dive site. Yeah, they are tricky at first, like a bicycle but one you get the nack it is so cool!!!!!!! I recommend now the Prowler 13 or Scupper Pro TW. The Scupper is faster, the Prowler a bit more stable and slightly shorter.
A 1300 dollar boat is immediantly going to become a 6,000 dollar boat because dude----dude----it is going to need a new engine, repairs, trailer work etc.
BUT, I also agree that if you want small boat get a Whaler. A 14 foot inflatable with a 25 horse engine is another option and will launch through surf and carry in a PU bed or van and will be more seaworthy than a 13 foot Whaler and easier to get in and out and will also cost you about 6,000 dollars or more.
Oh, a kayaks useful life is probably about 6 to 8 years (used hard and left outside a lot) unless very well taken care of. The material they are made from, rotomolded polyetelyene or similar products will eventually crack and degrade and UV degrades them as well. They can be repaired but at some point you just return them for recycling and get another---still--a very cheap dive boat. N