The calibration, service and certificate for Sprint V2 should be about £55.00 plus parts. (O2 cell is £45 and CO cell £75).
If you pay more than this, whom ever you send to may be passing on to one of the few authorised service agents. The calibration, supply of original manufacturers parts, firmware updates is controlled to companies that have been trainined and audited by the manufaturers.
Kane do not have any authorised service companies, all these unit we take to Kane, but charge the same price as Kane. they are 1/2 mile from me.
Testo have one external authorised service company so far.
TPI have only one external authorised service company.
Flue gas analysers are safety instruments, always use a calibration company that knows what they are doing.
If you want to ensure that the company servicing and calibrating any test instruments you have, ask to see copies of their training certificates. They won't mind, same as you wouldn't when asked to see you Gas Safe card.