Depending on what the job requires depends on the cost. Years ago(at least 10) Newmar had a recall that required ALL the sidewall area Sikaflex to be removed and new Sikaflex installed(The Sikaflex did not have the required UV inhibitor). The Average labor hours for that job on a 40 foot Diesel was 8.5 hours labor at then $100 per hour plus the Sikaflex. So, the warranty time plus parts came to just over $1000. This did NOT affect any roof sealant. So, just look at this example, do you really want to pay to remove the old sealant if new can be applied over the old and it looks good? If you cannot overlay the old, then expect to pay at least $1000 for a quality job or do it yourself. Doug