I think you shouldn’t judge the price of a product by compared to others, but by its usefullness for you. If you will use this lipgloss until the last drop is used up and you enjoy it all the way then I think it was worth it. Maybe if you bought the cheaper one you would get bored even before it is halfway through and would buy another one. In this case, the cheaper becomes more expensive.
So if you feel guilty about this spending you can justify it by using it as long as you can. And enjoy it! ☺