The gas inspection by Repsol is 65 euros every 5 years
Don't know about Cepsa.
These are the two main companies.
you need to contact them yourself.
don''t allow people who turn up at your gate purporting to be from Repsol etc, they may wear the uniform, have correctly headed papers, band indeed be qualified gas inspectors, but may rip you off, big time.
check the dates on the gas piping, and renew them yourself.