Annobanana and I hiked a portion of the highline trail. We had intended to start at the Drew Trailhead and hike down to the highline and then east to the 260 trailhead, but couldn't arrange to have a car at our destination, we hiked there and back. The section from 260 trailhead to See Canyon is the flattest and easiest part of the Highline trail. My friends who know tell me that this is the only section that can be ridden by a mountain bike.
You have four options to reach the cache:
1. Park at 260 Trailhead, hike to the cache and back, which is 7 miles roundtrip but pretty easy hiking.
2. Park at See Canyon Trialhead and hike up and back: only 3.2 miles roundtrip, but 600 foot climb/descent.
3. Park at Drew Trailhead on top of Rim (FR 9350) and hike down a very steep one mile descent of 1000 feet. You then hike back up that same trail. 
4. I recommend using two cars: park at See Canyon, then shuttle to 260 trailhead. The hike is about 6.5 miles, but you descend rather than climbing, and the best views are available this way.
To find the cache, go northwest 160 feet from the trail junction (can't miss: there's a fence) and look for a rock overhang as the hillside falls away from you. FTF gets a $1 coin.