Expect to pay 6-8p per ml for a decent wet lube that’ll perform well in all conditions. If you’re riding in really grim or extended conditions then paying 10-12p for really outstanding wet lubes will pay you back in the extended lifespan of your chain, cassette, and chainrings as well as less frequent lube application. Wax lubes tend to cost a similar amount too, but longevity payback depends on the brand and your riding conditions.