I think their ricing depends on if it is a prototype or production run. They can do multiple colors per side (4-20 sides). They have lots of options. Just email them details. I think a prototype run has a minimum of $50 buy for a few dice (no set up fee).
Yes, the price will be determined by how many sides you are customizing, rounded or square corners, possibly color choice, and the size of the production. The more you buy the bigger discount you get on their base price.
I think these are the base prices we started at. $4 for the 3 side custom one, $5 on the 4 side custom one, and $6 on the 5 side custom one. We then got like 30% off or something for ordering over 100 dice.
I agree with Ryan, I would just shoot them what you are looking for and they will get you a quote fairly quickly.