Katie, I think the whole permit, parking, etc thing is blown out of proportion. I've gone up there on a Labor Day weekend and got a permit without a problem. I went into the Visitor's Center at 11 AM on Friday for a Saturday permit, and including myself, there was probably just five other parties. Crowded, yes, Costco line for for a Polish dog or pizza, it is not.
The Horseshoe Meadows gets a fraction of the traffic of the Portal. You will not have a problem finding a space. I've been at the Horseshoes Meadows twice, and I've never seen more than two cars there, and it is a big place.
If you're really that concerned and want a plan C, get a hotel at the June Lakes area up North, or the town of Lee Vining (both near Yosemite's East entrance. The town itself is at an elevation of almost 7,000 ft.
Plan D is near Bishop at the South Lake Trailhead. That trailhead/parking spot is also near 10,000 ft. Can't help you anymore than that.
