If your looking at 4 - 5 K for a hull then I would choose a 4.7 meter Searider. I priced one of these up a couple of years ago and if I remember rightly it is in your price range. You will have a pretty unique boat, their aren't a lot around, its a very good sea boat and should be able to be made in to a flying machine with something like a 70 HP motor on the back.
I E Mailed BHG Marine to get prices.
The boats come with a small jockey and steering normally. You will also have to get a trailer from somewhere and obviously an engine.
I am convinced that if you can't afford a Ribcraft 4.8 then the 4.7 Searider is the answer for you. And it will make you Roguewaves friend for life.
If you want a secondhand 5.4 Searider there are plenty of ones around for about £2000.