if your life would be better if you had authorize.net payment gateway and US sales tax handling for the [url=http://www.silvercart.org/]eCommerce module SilverCart[/url], you should participate in funding these features. You thought the world would end in 2012 anyway, didn't you?
There is already one company interested in funding and we - as the module developers would also participate.
Total costs amount to ~ 2500 USD to implement authorize.net payment gateway and US sales tax handling.
In case you have no idea what SilverCart is: SilverCart is the most comprehensive eCommerce module for SilverStripe. It has proven to handle stores with > 400.000 products and is growing steadily.
You can [url=http://www.silvercart.org/hosted-demo/]get your hosted demo[/url] if you want to play around a little bit before jumping in.