The difference is that a Rolls Royce has status and prestige that can't be matched by Ford. And because they are expensive very few people have them. You cannot create the best price with a simple formula. If you do want to increase your prices perhaps you should consider raising them by a ridiculous amount. Obviously you would be selling to a different market and you must present yourself and your work appropriately.
Most people believe lower prices equal lower quality.
It's true the harder something is to get the more desirable it is. If your product is unique and desirable give it a price that reflects this. Uniqueness and scarcity have value. Your product is worth whatever the buyer feels it's worth, so find buyers who appreciate it's value . The message here is choose your market carefully.