Pricing is partially dependent on the amount of detail and variation you would like in your mural. A base-line calculation that I use for a simple mural such as the abstract yoga figures below, would be $5/square foot, plus a $35 materials fee.
If the mural requires more attention to detail, such as the bathroom mural with the tree, that would go up to $8/square foot. When including detailed, realistically styled people and animals, those portions of the mural are $10/square foot.
However, I am not a photo-realistic painter, simply a person who appreciates conveying a mentally tangible weight and volume to the figures I paint.