The most cost-effective way to repair a roof is to invest in preventative maintenance. Regularly inspecting and repairing small issues as they arise can help you avoid larger and more expensive problems down the road. Some simple maintenance steps include checking for cracks, loose shingles, or missing caulking around flashing; removing debris from gutters; sealing any exposed nails or holes with tar or caulk; and ensuring that all vents are properly sealed. Additionally, applying sealant to your roof every two years can potentially extend its lifespan by up to 20 years.
For bigger repairs such as replacing damaged shingles or installing a new underlayment membrane, it's best to hire an experienced contractor who knows exactly what they are doing vs DIY and taking the risk of further damage – this could end up costing you more money in the long run. Also, be sure to check for any local roofing grants that may be available in your area which could cover some of the costs associated with repairs.