Really really depends on the crack
Is it from hitting something? Or is it a failed rib or along a strake?
Is it taking on water? I've done a lot of hull repairs from jetty punctures or beaching
A few stringer repairs but when it's structurual you need to plan on possibly redoing more than just fiberglass and gel coat
All boats are a labor of love, major repairs are rarely worth the investment for resale IMO