Have a look at http://www.xs-ribs.co.uk
I've got a 6m on order with an optimax 135. They are quite cheap and the cost of my boat including braked trailer & pretty much every extra they offer (boat cover, double a-frame, nav lights, hydraulic steering, under deck loom, 110l tank & gauge, bilge, windscreen, seating for 5, VHF, paddles, pressure relief valves, etc.) is circa 17k (Boat Show Deal). They are new to the market and their hulls are based on the larger 6.4m Tornados and so should be rock-solid and great for coastal stuff.
This could be a viable option, and if you take away some of the extras I have, you would come very close to a your budget!
I'll post some pics when I get mine at the end of May. I think they have a 6m ex-demo available now.
Worth a look anyway. PM me if you have any questions