Humber make cheap and cheerful RIBs. They are OK, but tend to be a bit rough and ready.
Have you had a quick ring round to see how prices compare for 5m RIBs? All the contact details are here on RIBnet
! Let us know how you get on.
To be honest, if I was looking for a budget RIB I would probably opt for a second hand boat -- you'll get more for your money. With a 50 hp outboard, I wouldn't recommend anything over 5 metres though.