The problem is that my clever system of discounts is handy for getting people to spend more money in person while simplifying giving out change, but it gets ugly as more products get added. Complicated in person, and messy to program. And messy to change--I think I'm coming up on the need to raise my prices. It's been about 7 years since I've done that, and there's been some inflation.
The sticking point was quantity custom buttons (same as catalogue buttons if you get 25 or more, plus 15 cents/button for color printing) . mneme put on his evil programmer hat  and asked "If you order 4 catalog buttons and 24 of a 9 word, normal, custom button, how much do you pay?". At a convention, I'd decide it by feel, but this obviously isn't going to work on a website. If I say "Ok, just charge for 28 buttons", then a breakpoint has to be determined. If someone orders 4 quantity custom buttons and 24 catalogue buttons, I don't really want to just charge for 28 catalogue buttons. Or is it an equivalent situation? I probably just need to come up with a set-up fee for quantity custom buttons.
I realize that my customers' and my interests aren't completely aligned in this matter, but I'm hoping you guys will have some reasonable ideas.
Here's mneme's suggeston:
Would it be possible to recode the price structure as:
Buttons, stickers, little buttons: fixed price.
Custom buttons: Fixed price, plus a setup fee.
All: (except maybe setup fees) % discount based on either:
1. Number of items in the order.
2. Total price of the order (possibly discounting custom setup
It seems like a percentage discount based on the total size of the
order would make it more obvious to people how much they were saving
and maybe put the incentive back into the shopping experience.
If I go to this one, the discounts would be based on the total price, not the number of items.
 My thanks to dcseain for pointing out that Kinko's does much nicer color printing than Staples. Staples is Just Not Good Enough--the colors are changed too much--sometimes garish and sometimes muddy.
 I need some decent ideas for pricing, but I want some idea of what an evil programmer hat looks like.