Well, I would certainly avoid the big companies that advertise gold coins for investment purposes in the colour supplements and magazines, they tend to price way over the top. The price of gold bullion changes on a day to day basis, and the value of for example a sovereign will also vary depending on whether you are buying or selling. And if you decide that you also want your coins to be rare, or in particularly good condition there will be a collector’s premium as reflected in Coin Catalogues such as Spink.
I would strongly advise attending a coin fair such as those held in London, The Midland Coin Fair or the fair held in Yorkshire. There you will se a large variety of gold coinage at keen prices and can talk to bullion dealers and will enter the market with a far greater insight.
Jerry