If you are having trouble with the price of a gift card that is using the custom price option it sounds like you might be running into an issue that Woocommerce caused when updating the 3.0.0 version they are on. It changed some functions causing the price to just pass through not reflecting what the customer entered.
The most recent version (1.5.10) should fix it. If you have a current license just log into my site and you should be able to download the most recent version. Once it is installed it should resolve the issue that you are seeing. If the issue persists please let me know.