Best way to price something is Cost of Materials + Labour + Oh crap.
Cost of Materials-
This isn't just fabric, you also have to take into consideration your tools like scissors and pencils, your machines like your sewing machine, and even the power it costs to operate your machines, light and heat your workspace.
Labour-
This is always the hardest as so many people short change themselves. Look at it this way- would you work at a job for $2/hour? If the answer is no, then why are you making plushies for that price? Sure, maybe charging $20/hour is extreme, but find a happy medium. I believe that your labour wage should be whatever minimum wage is in your area. So if it's $8/hour, then charge around that. You must always be fair to YOU.
Oh crap-
Things happen. Waste happens. Mistakes happen. And especially- the customers needs can change. Always tack on at least SOME form of leeway to your work, that way, if some big mistake does happen, or more often, the client makes a change in the middle of the project, you're still covered. Any contractor will tell you the same thing, they always write this quotes with this in mind. I've worked with many contractors in a variety of fields from electrical, plumbing, carpentry, to upholstery, and they've all said the same thing, you always need to be prepared for "extra things". Usually they do a percentage (+30% of materials is common) so that when something does come up, they're not losing their shirts over it.
Remember, this is a business, and you (and your mother) are artists who deserve to be treated with fairness.