“Duct cleaning has never been shown to actually prevent health problems. Neither do studies conclusively demonstrate that particle (e.g. dust) levels in homes increase because of dirty air ducts. This is because much of the dirt in air ducts adheres to duct surfaces and does not necessarily enter the living space. . . . Moreover, there is no evidence that a light amount of household dust or other particulate matter in air ducts poses any risk to your health.” Cleaning your ducts may cause more health problems than leaving them alone. Just make sure you keep your HVAC filter clean and you should be fine. Spend the money you saved on a nice weekend getaway, that will do more for your health than duct cleaning.
https://www.epa.gov/indoor-air-quality-iaq/should-you-have-air-ducts-your-home-cleaned
Mike