Some Suggestions

[Little Sara]

Its pretty normal to make 10x of the amount you buy, if you go to a low level place. Tell me though, if you buy 100k worth of whites, or go Anubis with 100 Ygg leaves, where is your 10x profit there?

If I'm level 80 and I go fight Soldier Skeleton, I won't even need potions. But if I go Glast Heim, potions won't let me survive even if I buy a ton.

If you fight challenging enough enemies solo, you should make ~2-3x your cost in loot. If you do it in a party (especially with a priest), your cost should go way down, but you split the loot, so it's still less.

If your only way to create zeny into the economy is finding rares, then at some point only a select few can even buy what you sell, others would be too busy surviving with their pots. Or people would ditch item hunting and go mining 24/7 for cash.