I don't think it's so much the sale price vs actual value that would be unethical. You can set your price at whatever you like and it's up to people to decide if they want to make that deal. There are tons of things that are overpriced.
Where I see ethical concerns is when you know somebody doesn't understand or know what they're getting (selling someone something you know they don't need, selling fakes, not disclosing certain information, and so on).
Another would be taking advantage of someone's despair in time of need (selling food at ridiculous prices when there is hunger).
So if it's just that you got a good deal on something and sell it higher, power to you. There is a ton of business that operates under this principle. If the items are unique or rare, then really your profit can be considered the fee for finding and preparing the items. $1-5 is quite a low profit margin, too.
