Separately icon/letter minimum character and pricing rules

Separately icon/letter minimum character and pricing rules: I don't want to burden my customers too much for adding an icon, only a maximum of €50-100 per icon. However, if a customer orders just one icon with a size of 100cm, the price would be around €100, which is way too low. On the other hand, if the customer orders a text with a length of 100cm, which already costs €500-600, and then adds another €100 for the icon, that would be acceptable. I need to set the prices for the icon in such a way that if a customer orders just an icon, they would be around €300 for a length of 100cm. If I add this to the €500-600 range, the price would be too high for the neon sign and no customer would buy it.