Pricing is an art, not a science.
There’s no fixed answer to the question of what price to charge. The answer is a massive “it depends”.
You only have to look as far as something as near-enough universal as soft drinks to see this.
The unit size can affect price – soft drinks are generally more expensive per litre the smaller the serving size but that’s not always the case.
For instance, where you’re buying your drink will affect the price as well. Supermarkets are generally the cheapest, elsewhere the price will vary.