Mine is an ex AA van 1999 model and already converted by previous owner, tin top, alloy wheels, cupboards, sink, leisure battery, electric hook up, r&r bed etc and registered as a motor caravan, I know its a conversion and not built as a camper from new, but it was less than 5 grand. I don't know what you get with a cali, check number plate on
https://www.vehicleenquiry.service.gov.uk/Default.aspx to see what the VED is, mine is a 2.5TDI with intercooler but because it is pre 2002, VED is £230 per year. The rules changed in 2002.
I only bought this two months ago, it has 193,000 miles on the clock but I am told that is less than half of what the T4s are capable of. Hope this helps.