The value of any memorabillia is the price someone is prepared to pay for it, which can vary considerably. Your best bet is to buy a copy of 'Record Collector' magazine, and check out the ads in the back - there are plenty of memorabillia collectors and auctioneers who advertise, they will usually give a rough estimate over the phone. Remember - dealers usually look for 100% mark up on what they pay to buy, as against what they sell, so that should give you an idea of prices. Check out the small ads for private collectors - someone who specialises in Queen discs etc. may be willing to offer you a good price.