Licence plates were removed and the Saab burned
The 34-year-old was shot in the back as the group of off-duty servicemen tackled four masked robbers who were holding up a security van at a motorway services in Warwickshire.
The incident began when the group of soldiers spotted the robbers threatening a female security guard at Tamworth services on the M42 last week.
Eight of the party, from Lincolnshire, tackled one of the robbers and wrestled him to the ground but one of his accomplices fired at the soldiers.
A 34-year-old member of the group was shot and the servicemen were forced to release their hold on the robber.
Warwickshire Police believe the gang escaped in a silver Saab which was later found abandoned and burned out in Tamworth.
Detectives are keen to hear from anyone who saw the Saab being driven to the location near the Snowdome in Tamworth, or who saw the occupants leave the car.
The security company that owns the van has offered the reward after it revealed a substantial amount of money had been stolen during the incident.
Warwickshire Police said the soldier, from 22 Regiment Royal Artillery, also known as the Welsh Gunners, suffered serious but non life-threatening injuries.
He is recovering at the George Eliot Hospital in Nuneaton.
The victim was among four coach loads of soldiers from the regiment's base in Kirton in Lindsey, near Scunthorpe.
They were heading to Wiltshire to watch an army rugby tournament final.