payment gateways and accurate shipping quotes

Hey there,

One of my clients wants to accept payments for a product he offers.  The thing is, he needs accurate shipping quotes based on the shipping address.  I looked into paypal and while you can prepopulate forms using POST name/value pairs, it turns out accurate shipping quotes are only available to U.S-based merchants.  So scratch that.

He then told me to look into authorize.net to accept payments.  It seems great on first glance but I can't find any option for shipping quotes other than using third-party e-commerce packages.   That would require me to dive into the API and I'm not prepared to do that until I figure out exactly what I'm doing.

So, any e-commerce whizzes out there?   I'm in a 2-year web programming course right now but we don't get to e-commerce until the 4th semester so the timing of this sort of sucks.  He's the client and he wants what he wants.  With a little help I'll just have to pound this thing out.

Any considerations are much appreciated