Martin, I would have thought that you could pick up a new engine with considerable discount on list price at this time of year. With a 12k budget, you should be able to rig yourself out with a bit og haggling to get a basic spec hull with a good quality engine and still get afloat. I agree that boats are easy to upgrade and add to as time goes by and money become avaiable, but start with a good hull and tiptop engine. If you want to cruise longer distances, most are currently fitting 4 strokes and there are many models coming onto the market. That said, the new generation 2 strokes are streets ahead of what you could get event a couple of years ago. If your prepared to wait a while for the hull to be built, so that you hit the quite season, you should do pretty well.
A good deep V hull will be needed for open crossings. Think about fuel and kit storage, crew numbers, whether you want a work boat or a gin palace, etc. Go for a manufacturer that has a reputation in the type of boat you want, rather than one that predominatly does something different.
A word to the wise - my experience is that you quickly outgrow your intial expectations and can end up with a boat, that was good to start with but a bit lacking when your experience and confidence grows.
Oh, yes and you need to think about the colour!!