Your coin is old enough that it is starting to pick up some numismatic (coin collector) value over and above its basic gold value if in good condition. To figure a retail price for your coin, start with today's gold bullion price of $1340 US dollars per troy ounce and multiply it by 0.2354, the number of troy ounces of gold in a sovereign. That gives $315. The price of gold changes daily, so look it up at web sites like kitco.com.
To the base price now add about $80 for the coin collector value, giving $405. That is the retail price, what a collector would pay. If your coin were in beautiful, fully uncirculated condition, the $80 would about double.
If you want to sell your coin, that is another story. Dealers charge commissions on coins they buy in order to make money when they sell. For your coin, a $100 commission would be reasonable, so your selling price would be $405 - 100 = $305.
There are a few low-mintage dates in this series of coins where the numismatic value goes through the roof. If you have one of these, you have a special coin. The dates are 1838, 1839, 1841, and 1874.
The US dollar is weakening dramatically. Pricing of gold coins is all over the place these days. This applies to both buying and selling. If you are serious, be sure to shop around for the best deal. You also have to be careful about counterfeit coins. Dealing in rare coins is a *buyer beware* proposition.