IIRC, there was a window of about a year prior to the R2 release where, if you bought 2003, you were entitled to a free upgrade to R2 but, aside from that, it's a new product and you'll need to buy it.
I think your only recourse would be if you purchased 2003 shortly before the release of R2 and your retailer didn't advise you of the free R2 upgrade offer (you had to register with MS for it).