How do I handle SSL in Multisite with subdirectories, ProSites, Marketpress and events

I am developing a multisite with subdirectories. What is the best way to handle SSL? I would like the registration page, and the ProSites, MarketPress checkout as well as any events for a fee to have SSL protection. Does a single SSL on the primary domain cover all of these instances or do I need to get separate SSL certs for the subdirectory sites?