You'll want to look into roto-molded boats—plastic boats—and avoid carbon, which is more expensive. Roto-molded boats are tough, long-lasting, and moderately priced.
The next step is to look for a style of kayak labeled “recreational.” You don’t need or want a whitewater boat, nor a touring boat. The best choice will be a boat you can hop into and paddle around with a minimum of hassle.
In this class, the Perception Prodigy is a great start. At ten feet, it is wide and stable and was designed for lakes and slow rivers. It has a roomy cockpit, and a hatched storage area in back for a few daytrip supplies. And at $500, it’s pretty affordable. Also check out the Wilderness Systems Pamlico 100, which is similar in size and specs and costs $550.
For something just a bit sportier, there's the Elie Sound 120 XE. It’s two feet longer than the Prodigy, making it faster and allowing it to track better. It’s also got a stiffer hull and some nice touches, like a bottle holder. Its big cockpit and hatch offer great stowage capacity, and you could even could take this boat on an overnight lake trip. It comes in at $750.