Unless you are only doing this with service work or a particular type of work that isn't ordered at varying times of the year, I'm at a loss over how you or your affected customers can justify even slightly different pricing based on YOUR level of busyness. Our overhead costs except for cost of goods are pretty constant throughout the year, so our rates and pricing is based on that.
I'm not trying to be this dense about it, I'm just trying to picture the conversation when you tell someone you did a 4'x8' in March for $450 that its now $600 because you are swamped.
I have a base price for most things. My base for 4x8's single side is $495+install. Two or three months ago I started getting overwhelmed so I rose it to $595... everyone gets that price UNLESS its a
regular customer that
routinely orders 4x8s... then I keep them at the base price. If I keep going at this pace and can't control the work coming in, I'll raise the base and
everyone pays that new price.
On the flip side, if I start slowing down I'll adjust the "surge" price back down. Over the last few months I know I've been loosing sales of 4x8's which is fine... it's what I needed to control the amount of work. Of the ones that bought my 4x8s at the higher price, they got exceptional service and 3-4 day turn-around instead of 2-3 weeks at Slow Signs.
I'm a one man show so I know what my past customers routinely order.. You'd have to figure out how to make this method work for your shop having multiple people.
As equipaint said, labor is easier to mess around with.