Private companies have ambulances as well, we got rid of an old one with barely any miles on it
That's often not a good thing. Our power station vans usually get scrapped at about 7-8 years old with a few thousand miles on them. Because they've spent their whole lives trundling around site at 15mph, never getting warmed up the engines are absolutely ****ed. Probably get above 2nd gear once a month when they need filling up with fuel.
Best buy (if you could find one) would be a major incident response vehicle from an NHS Ambo service. Minimal miles (major incidents are few and far between) but kept in a full state of readiness, and serviced as per manufacturers specs. Sometimes (though not always) garaged, too.
Edit;
Bit over budget, but this could probably fit the bill (never seen a smelly patient in its 25k mile life, either)
https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F264408691203
Or a HART vehicle.
It’ll still have the rubber tags on the tyres.
Do you honestly want to be sleeping in an old ambulance, knowing many many people will have drawn their last breath in there. It would undoubtedly be haunted..
id just buy a welfare van.....
Rock up with your camper, lower the legs, unhitch the pod, drive to the shops.
Like this, you mean?
[url= https://live.staticflickr.com/65535/48476004112_f80a06ce4d_o.jp g" target="_blank">https://live.staticflickr.com/65535/48476004112_f80a06ce4d_o.jp g"/> [/img][/url][url= https://flic.kr/p/2gREc9m ]Weird camper thing[/url] by [url= https://www.flickr.com/photos/40141861@N00/ ]tillydog[/url], on Flickr
Like this you mean?
I was thinking more like this, but with wheels

Perchy dont be daft. Why would it need wheels if it can fly ?
Why would it need wheels if it can fly ?
To get it through a car wash , obviously.
That command ambulance thing is amazing, if I had the cash to spare I'd definitely go for that! 170+ bhp too, so would probably do more than 17mph up a hill unlike my mate's Bongo 😂Bit over budget, but this could probably fit the bill (never seen a smelly patient in its 25k mile life, either)https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F264408691203
The same guy on eBay also has (much more reasonably at £10k) an old mobile library vehicle which would probably also make an awesome camper!
I've been looking at these starting their deliveries for the day from our local depot as I drive to work recently. Reckon they'd make an absolutely ideal base for a home-brew motorhome.

Seems the price for a Police or Welfare van Merc Sprinter is about £10k-£12k
Another option is buying an older pro-converted van and doing a refurb. However with an already converted van, you get much less choice on the layout.
I really like Mike_D's layout

Ups box vans are dismantled and recycled.