A lot depends on condition of EPDM and your budget. If you're a die hard DIY'er, installing a new EPDM membrane is not that difficult and should last many years. Cost would vary by area and supplier but $300 is probably a good target for DIY.
Coatings are just that, a paint basically, that is applied to the surface and will change appearance and offer some UV protection. I sprayed my aluminum roof with an acrylic elastomeric roof paint and it is holding up well at five years (stored outside). I used White and it lowered the cabin temps by 10f. Typical elastomeric roof paints cost in the neighborhood of $30-> $50/ gallon. Do two coats.