What country are you going to register it in? Are you resident in EU country yourself?
If you are going to buy it from Spain but register in some other country, there might be import fees and taxes in addition to regular registration costs.
Also insurance depends on country where you are going to register it in, both in difficulty and cost.
As an example here in Finland you cannot register it as a van if it has fixed furniture inside (allowed are shelves for cargo transport) and if you want to register it as a motorhome there are minimum requirements (beds, seating, and tables for two, cooking etc) that it has to meet. After you have managed to register it as a specific vehicle type, the clerk at the registration office will just ask what insurance company you want and what level of insurance and it’s done. At this point it’s best to choose the top tier one possible and once you get home call the insurance company to get a specific one for your situation. They cannot deny you from the basic insurance, since it is mandatory. Voluntary insurance is different thing, it might have high rate and/or some special terms.
It totally depends on what country you are in, so it is impossible to anything for sure.