1999 gastly pokemon card value 50/102 Like new [P] Sleeping Gas 1999 Pokemon Base Set Shadowless

TRR 86 1 Boss's Orders RCL 154 1 Pokmon Fan Club UPR 133 2 Pok Ball SUM 125 2 Switch SVI 194 2 Ultra Ball BRS 150 1 Rare Candy SUM 129 1 Super Rod BKT 149 1 Super Scoop Up BUS 124 1 VS Seeker PHF 109 1 Scorching Charcoal CLC 26 2 Computer Search BS 71 Energy - 16 7 Basic Fire Energy CLL FIR 7 Basic Lightning Energy CLL LIG 2 Double Colorless Energy BS 96 Visual Card Breakdown Charizard Deck Set List Charmander (Base Set) Charmeleon (Base Set) Charizard (Base Set) Ponyta (Astral Radiance) Rapidash (Astral Radiance) Magmar (Fossil) Ho-Oh ex (Pokmon TCG Classic) Pikachu (Base Set) Raichu (Sword & Shield) Voltorb (Base Set) Electrode (Base Set) Zapdos (Sun & Moon Promos) Clefairy (Base Set) Clefable (Jungle) Stantler (Secret Wonders) Miltank (Secret Wonders) Dunsparce (EX Sandstorm) Bill (HeartGold & SoulSilver) Boss's Orders (Rebel Clash) Computer Search (Base Set) Pok Ball (Sun & Moon) Pokmon Fan Club (Ultra Prism) Professor Oak (Base Set) Rare Candy (Sun & Moon) Rocket's Admin

How do I find out what my own Pokemon cards are worth

Too much

It is unknown if this feature will be returned later or if some other system will be released to replace it