Hello Martin,
Welcome to the Forum.
I respectfully suggest you do some more research on conversions, and their cost.
Firstly you need to decide what type of conversion best suits your needs.
What equipment will it need, bed, fridge, cooker, sink, toilet, etc. etc. Pop Top alone will be £4k or more.
Some convertors are better than others. Many only work on vans they source themselves.
The better ones tend, unsurprisingly, to charge more, and many are registered for VAT.
Don't forget to budget for the VAT !
The better convertors, that will work on your van tend to be very busy, so enquire about conversion leadtimes.
Sourcing parts has become more difficult this last year or so too.
There are many members who have imported their own vans.
Hopefully, some will respond to your thread.
Good luck with your search.