The rewards state "Shipping to the US and Canada are included here -- no further payments will be necessary to ship to those countries."
What this means is that $20 is charged here on Kickstarter for shipping, and further payment means after the campaign. So you only pay $20 now, and nothing after, if you are shipping to USA or Canada.
International customers (not US or Canada) will pay around $60-80 after the campaign ends and when we get a better estimate on shipping.
Please see the shipping section at the bottom of the campaign page for more details!