Just to suppliment already what has been said already if your cat jsut has the one sensor before the cat then it will run fine without it infact you should see a slight increase in power due to lack of back pressure, cats generaly cost around £500 from the dealers but after market manufactures are starting to make them now and the prices of these are coming down. I have a 2.0ltr mondeo with a performance manifold, exhaust and no cat and it passed at my local garage figure that lol.
I do know though that the cat is only responsible for reducing the emmisions by quite a small amount and as your van is a 95 model then the emmisions applicable for that year arnt that strict so it may well pass without the cat in place.
With regards to price £450 for a full stainless system is about average but you have to bear in mind that A it will probably add to the value slightly and B you will never have to replace it every couple of years as it wont rust
