Is $600 to replace two leaking roof vents with a different style a fair price?

The quote is to replace two existing roof vents that are actively leaking. The current vents are a style known to leak, especially one over the kitchen vent hood which caused a waterfall. The roofer will install a different, more reliable style of vent. Both vents have ductwork connected (rigid for kitchen, soft for the other). - Scope: Replace two actively leaking roof vents - Reason for replacement: Current style is "known to leak" - New vents: "different" style to prevent future leaks - Specifics: One vent is for the kitchen hood (rigid duct), the other's purpose is unknown but has soft ductwork connected - Condition: No leaks or wetness found in the attic decking around either vent