The best approach to determine card costs is to use this app's price checker for cards here (https://collectorpricing.org/pokemon-card-value-finder/). And cards are only worth what someone is willing to pay. Your cards are very valuable when taking into account player surveys, eBay pricing, and Pokemon prices. You can see that they have a sizable collection of cards on eBay. You may learn about card costs in Pokemon pricing, including if they are rising or falling.