The owners put up the reward after the two vehicles were damaged in a suspicious fire at the Bus Depot ABC Travel in Clarebrand, near Castle Douglas at around 1am on March 23.
The money will be issued to anyone who provides the information that leads to the identification and prosecution of the person or people responsible for the fire.
A Daf recovery lorry and a 56 seat single deck coach were both discovered well ablaze on the early hours of that Friday morning. Fire crews attended and extinguished the fire and following a joint police and fire investigation, it was established to have started suspiciously.
The cost of the damage has run past £150,000 and both the owners and the police are keen to find the people or person responsible.
Detective Constable Ross Milligan from Castle Douglas CID said: “We have conducted a number of enquiries, including staff statements and a door to door of the surrounding area.
“A number of lines of enquiry have opened up however we need more substantial evidence to pursue a positive line. Whilst the fire was serious, thankfully no one was harmed in it.
“It did however cause a considerable amount of damage and we are keen for anyone with any information to contact us. No matter how little it is, it could be the missing part of information we need. Did you see any suspicious behaviour in the lead up to the fire, any vehicles that seemed to linger or people you don’t know? If anything springs to mind, call us on 0845 600 5701.”