Hi Mark, welcome to the forum.
From the photo it looks like an early 80's or late 70's van and I'm guessing a Triton or Troll. Mint versions could make £6K to £8K if you found the right buyer, but it would appear from your photo that you could spend that much getting the Eriba in question up to that mint standard. A rusty chassis/framework for example could easily make the project a no-go.
I would think low £100's as it is a big risk and a labour of love. If the van was not worth renovating then you would probably be able to recoup your money by stripping it for parts.

Colin