Vehicle "common/constant" power go to relay pins 30+pin86 Vehicle switch/earth trigger (low beam or high beam) to pin85 Relay pin 87 to either high or low beam connection on LED LED earth to custom earth.
@@knobblyknob relays are way cheaper than that. Where are you buying them? You can pick up a decent number on aliexpress for pretty cheap. Just watch out for the ultra-cheapies