If a company that sold implementations of and support of open source products were subjected to this kind of sales cycle for its services, then it wouldn't cost any less than closed-source products.

IBM Global Services will happily rip out your "legacy" infrastructure and replace it with nice shiny Linux. But not for free... And when the dust settles, it's not going to be any cheaper than if they did the same job with AIX (why would they leave money on the table?)