How can this be an issue if their base software is open source? Just recompile it with the numbers upped, surely?
For people like me that already rent a VPS for their mail and website the marginal cost is $0 except for the time it would take for me to perform the installation and setup.
If the system is good and stable then the "cost" of the time that I would spend installing it on my server would be close to $0 when divided over the amount of time I use the software in the future.