one silver = 100 copper
one gold = 100 silver
one gold = 10,000 copper
And about the prices for the Auction House... Maybe try selling a stack of 20 Earthroot for 75 silver, Peacebloom for 40s per stack of 20, and a stack of 20 Silverleaf for around 25s per stack. You should try selling Mageroyal for 50s (or 50 silver) a stack, and Briarthorn for 2g and 25s (2 gold 25 silver)... A good way to find a reasonable price for any item is to go to the website wow.allakhazam.com and search for the item. Then it will show a picture of the item, under it it will say the median price, but go for the "Most Common" price. You will be able to see the most common price for one single item, but if you are trying to sell a stack you should look for "Price Per Stack," which will tell you an estimate for a complete stack of the item (If it is a "Stackable" item). **BUT** this is just an estimate... the prices on that website are all of the servers combined. Every server's economy is different. For example, I have a rogue on Medivh, and also a priest on Shadow Moon. Traveler's Backpacks are worth 13-16g on Sahdowmoon, but only 5g on Medivh. I hope this helps a lot, and good luck to you!