You can get away with renting one car and parking it at the Crescent Meadows when you start HST. There is a very expensive option of taking a shuttle from Whitney Portal to Crescent meadows costing around $800/-.
Other alternative is take a taxi (to be pre-arranged) to Ridge crest (may cost around $100/-) from Whitney Portal and there rent a one way Hertz rental (Ridge Crest to Visalia) - which may cost around $50/-. Drive to Crescent meadows, pick up your original rental and return the Hertz rental in Visalia. This presumes two drivers in your party.
For taxi service in Lone Pine, there is lot of info available in these chat pages. I recently (in July 2014) did HST and was lucky in having two San Jose cousins help me out - one dropping me off at CM and one picking me up at WP. We also did the alternative 2 above a few years back and it worked out well as we both are drivers.
