I've dayhiked Langley twice, once sleeping at the "old" part of the Dow Villa Motel, once at the Horseshoe Meadows trailhead, for hikes in August and September. As of 2008, if you get there early enough Friday and it's not a popular weekend, there will be great tent spaces available at the Meadows.
Do you have a truck? You can sleep in the back at Horseshoe Meadows if you are inconspicuous. Be sure to put your smelly stuff in the bear boxes (including soap, sunscreen, toothpaste) overnight. It can be quite cold at night, so if you don't have a sleeping bag, bring plenty of blankets/quilts! I've been comfortable in the front passenger seat of my Outback, after I reclined the seat way back, used a neck pillow, and put something under my feet.
The old part of the Dow Villa has a variety of cheaper rooms, depending on whether you want your own attached bathroom. The walls are thin -- use earplugs. This is a popular place -- book ahead of time.
Weekdays best for both options.
I've never stayed at the Whitney hostel -- look over that option: http://whitneyportalstore.com/forum/ubb ... #Post51019
I once loved hostels. Just 4 beds to a room sounds great. Caution: try to arrange compatible waking and bed times, or again have earplugs. Some folks like to go to bed late before a climb; some like to wake up at midnight and start packing. I snore so badly, that I longer feel good subjecting other people to my presence.
It's a long dayhike -- well over 4000' accumulated gain at the end of the day, because there are a few ups and downs, even through Old Army Pass, and 19 miles RT -- but easily handled in a day IF YOU ARE IN DECENT CONDITION.