Firstly this is not an advocation for the Pirates to acquire Rasmus. I think it's safe to say Cardinals wouldn't trade him within the NL Central and certainly wouldn't trade him to a team who has even an outside shot at competing for the division title.
However there has been discussion about acquiring Rasmus over the last year or so, thus I thought I'd link to this article on ESPN that hints at what the White Sox, who are evidently interested, might have to give up to get him. Reportedly Edwin Jackson or Matt Thornton and a prospect. Of course you don't get a sense of what sort of prospect, which is an important detail.