Been to a few Van & HGV auctions, don't disregard a non rusty Sprinter (the non rusty bit is important) mate of mine is rocking an 05 plate 308 CDi 2.2 which he paid £2k for back in 2015 - at an auction - , it now has just shy of 700k on the clock and it drives very very well, the trick with them is buy one thats battered, not rusty, his looks like its been vandalised from the inside out but mechanically its spot on.
A weekend tidying up the numerous outward pointing dents and it would look fantastic but have a price to reflect this....
Merc trucks are dire these days unfortunately, but, their vans are very good imo.
Certainly get you looking at Relays though, theres a reason they are commonly used as ambulances and it isn't because they are relatively cheap, let down by stereotypical French electrics alas (although not ex ambulances as I believe they have extensive re-work of the electrics during conversion which kind of makes sense)
Despite the above, Amen.