I don't want to offend you with this Riot, but i know you will make fees anyway:
For emotes,wards & icons- 250(all cost BE);
Skin shards- 750;
Skins- 1000 for the cheapest(+ 50 for each next rarity(1400 on ultimate));
Crafting materials(without hextech chests)- 1500.
When it's exchange between to players, the fee includes only one item and it's divided equally for both.
I didn't put keys, because you can earn the very easily(at least i can about 2 key fragments/day).