What is the best way for a sole developer to have access to a SharePoint 2010 installation for testing administration and development?
I would say download the Foundation version of SharePoint (which is free) http://technet.microsoft.com/en-us/sharepoint/ee263910.aspx#tab=1 and install it on either a physical or virtual windows server.
If no server available then install it on your vista or windows 7 machine, note that it must be a x64 machine. Here is the official guide, http://msdn.microsoft.com/en-us/library/ee554869(office.14).aspx
Stay away from cloud solutions, SharePoint consumes a lot of performance and need an entire server or computer for it self, otherwise it will be a painful process of learning and developing for SharePoint.