Hi Gramma! These are beautiful coins with plenty of numismatic (coin collector) appeal. They contain 0.4823 ounces of pure gold. As such, you can compute the bullion value of the coin by multiplying the spot gold price by 0.4823. Let's say the current price of gold is $1150 per ounce, that's about 0.4823 x 1150 = $555 US dollars base value for the coin. Use a web site such as Kitco.com to get the current price of gold. It changes every day.
This coin is old and beautiful. That means it carries more than just the basic gold value. It carries numismatic (coin collector) value as well. The better the condition, the more numismatic value.
Gramma's coin is authenticated, graded, and encapsulated by NGC, a highly reputable coin service. This adds to its value. The AU58 grade means it is just shy of perfect uncirculated. This, too, adds to value.
If Gramma's coin were worn, or cleaned, or full of stains and spots, the numismatic (added) value would be about zero. My guess for the 'addition of value' to Gramma's coin is about $35, making the coin's total value about $590 at the time this appraisal was last updated. In a good eBay auction with lots of bidders, the coin could easily pull over $650. It would never go for less than the basic gold bullion value.
Gold dealers generally charge a small percentage commission to buy and sell gold coins. If you are selling, subtract the commission from the raw value above. If you are buying, add a commission. Shop around for the best commission.
All the dates in this series of coins carry about the same value as Gramma's.