I just spoke to Group2 Motorsports in Seattle - they said they've done a couple E9x M3 rod bearing replacements.
Was quoted 9-10 hours labor at $125/hr, so $1125-$1250 + tax for labor. Part cost would depend on which brand bearing the customer went with. If you have them order the parts directly, you get their 1 year/12K mile warranty. If you supply the parts, no warranty.
I've never had work done there but heard great things about them.
http://www.g2motorsports.com