Shut-up And Pay
Can I suggest that one of the reasons why SAP are so reluctant to publically reveal these things is that not everyone is paying the same price; and there would be a lot of very unhappy people when they realise that they are paying hundreds of dollars per user more than other businesses.
As for open source systems; they will often work for smaller businesses. However, once you start talking about multi site, multi country operations with 10s of thousands of employees, you are in a whole new area and many of those FOSS / FLOSS systems are just not up to the job.
Developing internally is not a bad option, but you have to have the right people that can identify the real requirements and then have skilled programmers that can do the job right. There are a lot of people out there that think they can do it; I know from experience, that there are an aweful lot who are nowhere near as good as they think they are.
When you buy SAP, you have committed a lot of money and resources to the project. That's why so many are reluctant to jump ship; they are scared that they will end up wasting more than they gain. SAP know this and that is why they will keep squeezing the customer's teats to get those last little drops.