Welcome.
My thought process was similar for my previous van as I wanted a Kombi and had no intention of converting to a campervan. So I bought a panel van, removed bulkhead and fitted side windows, genuine rear Kombi seats and belts and a single front passenger seat and base.
Rear seats, brackets, reinforcing plates and belts were approx £1000
Single front passenger captains seat with base was another £1000
Windows were approx £500
With other bits and bobs e.g. tools to take out the bulkhead it came to £2600 - fitted by someone would have added another £500-£1000.
With my current van I bought a factory Kombi as it still gets used the same and is still not a campervan. It was literally 3 years old to the day when I bought it and I estimate I paid approx £5K premium over a panel van of the exact same condition, spec, age and mileage.
So yes, it is slightly cheaper to buy a PV>Kombi over a factory Kombi.
But, for me, having done the conversion once I couldn’t stomach doing it again, so wanted to get a factory Kombi that was ready to go so the extra spend was more than worth it to me.
*I have left off the cost of deadening, insulating and carpet lining as I did this on both vans.