How can I find out what amount of money gear costs? For example, "Hide Armor costs 50 gp." How much would Potions and Tools cost?
If you don't have a copy of the Player's Handbook, you will probably be pretty lost in the game, as it will answer hundreds of basic questions of this sort for you. It's available at various friendly retailers (physical or online).
Potions beyond the potion of healing are considered magical treasure and the prices are in the Dungeon Master's Guide, but your DM may control their availability and price. (In fact, you should ask them about normal equipment too, just because it's in the PHB at a certain price doesn't mean that necessarily holds in their game world.)