As you are based in Victoria, you will not enjoy the news that we have the toughest Energy Safe compliance regulations in Australia. Coffee companies who have moved operational roasters from another state to Melbourne have been reduced to tears when they discover they can't hook up their relocated roasters without sometimes extensive modifications At best it may be as low as $2K for just the compliance work which excludes any parts that could require change or addition. Allowing a budget of say $3K for a small simple appliance is typical. This covers the review of electrical and fuel schematics, advice on modifications and all the labour associated with testing of airflow and purge rates, over temp controls and fire suppression systems. Submission of approvals and final testing with or without an ESV inspector present. Assuming a gas system, if the pilot, mutlibocks, purge timers, air and gas pressure switches or burner are not AGA standard, they will need to be replaced with compatible devices. Not excessively expensive but annoying and frustrating. Similarly, external mechanical proving switches are required for safety interlocks which are almost never designed and fitted at the factory. I am with A. On this one. If it is a gas appliance and you don't know what you are doing or have not worked through and ESV commissioning exercise before, suggest engaging an agent.