Blue Sapphire gives best result in iron ring, then in steel and finally in panch dhaatu (five metals). Silver is a strict NO as silver signifies Moon, enemy of Blue Sapphire (Shani/Saturn).
Quality does not depend on price at all, price depends on quality. Always buy gemstones that are certified from reputed gemological labs.
Wishing you good luck, may God bless you and over all!