The incident happened in Baildon at about 11am on 10 April, when the victim had travelled from Cleckheaton to a private address in Ashfield Drive.
As he pulled up outside the address he opened the boot of his blue Ford Focus and was approached by a much younger man who engaged him in conversation.
The man then snatched a bag from the boot which contained a significant amount of cash and ran off.
The victim gave chase but the suspect jumped into the passenger seat of a white Ford Transit van in Kirkfields.
The van drove off towards Station Road.
Investigating officer Detective Constable Simon Turton, said: "We have carried out numerous enquiries into this high value theft of cash, which the victim had taken out to purchase a vehicle later that day.
"We believe he was followed from Cleckheaton after withdrawing the money from a bank in the centre of town at about 10am.
"We would like to hear from anyone who recognises these men, or anyone who may have seen them in Cleckheaton or Baildon on that day.
The suspect is described as white, aged in his mid to late twenties, about six feet two inches tall and of stocky build.
He had dark stubble and was wearing blue jeans, a full zip hoody in light grey and a dark coloured baseball cap.
"Our enquiries are continuing and anyone who can assist these is asked to contact Bradford District CID on 101, quoting crime reference 13170162065.
"Information can also be passed anonymously to the independent charity Crimestoppers on 0800 555111."
Ashfield Drive, Baildon, BD17 6JA