In reply to dan bailey:
Take care. Don't buy the first apparent bargain you come across. It could be a fast tippy boat that only experienced paddlers can handle.
Plastic boats are usually cheaper and more robust. The Prijon Yukon and other Prijon boats are incredibly stable and forgiving for beginners.
You don't get bargains on ebay. You'll pay through the nose for a sea kayak on there. Put a 'sea kayak wanted' ad on the paddling forums. I picked up a great little 'Necky Looksha' fitted with a rudder for my son from an outdoor group which had been used once after posting an ad.
For a total novice try and get a boat with a skeg or rudder. It makes life easier when you're trying to track...go straight.
'Real' Sea Kayakers frown on rudders and prefer skegs but they make life easier for novices.
The real deal expedition SK's tend to be fast fibreglass boats costing up to £3k new, You can pick up cheaper 2nd hand ones.
I'm trying a P&H Sirius that a friend has but I'm told it's quite tippy having a narrow hull.
It's a fantastic activity that seems to draw in a lot of climbers of a certain age....well middle age actually !
Have a look at the Scottish Sea Kayaking site run by Douglas Wilcox. If those photographs and trip details don't make your mouth water then it's not for you.