Hey man, you should check out Troll and Toad, the most popular card singles marketplace for buying and selling pretty much every relevant card game. You can search the Fossil set by clicking:
Pokemon -> All Pokemon singles -> original series -> Fossil unlimited singles
Or you can just click here to view this page. From there, you can search up any card in the search bar under where it says Keywords. Type something like Aerodactyl in and it will show you two pages for Aerodactyl, a holo and non holo variant both worth different prices and it will show you other competing websites in case someone else is offering it for less or in better condition, which will ultimately affect the value of your cards. You can do this for any card, any set, any game.
If you want to know a good way to determine the condition of your cards, read this article.
How much is a whole set worth if you sell it as one you may ask? On ebay, you'll probably be looking to spend at least 300 for a near mint collection. I would just keep your collection, it's a cool piece of vintage 90's memorabilia history. I wish I had kept all my old cards all these years later.