Forget DIY shuttles: Diamond Creek is not an option unless you want to pay (or have a VERY good friend) someone to come in and get you, and it's $65 per prson/vehicle/etc. It is "not recommended" to leave vehicle at Pearce and there's no place close that's safe, either. I've used River Runners Shuttles (used to be Wes Montgomery, believe it's his son or other family members now) and they are not only reasonable, professional and kind but offer secure storage at Meadview (close to Pearce).
Last suggestion is to contact one of the commercial companies that has a trip pulling off around your takeout day and see if you can work out a deal with them for transport at least back to Flagstaff. Most deadhead to Pearce and there's plenty of room on their rigs for some kayaks, IF you can work something out. Check various websites and call them - you might just get lucky.
It's another 54 miles from Diamond to Pearce, but right now rapids down to 234 or so and current all the way past the boat ramp.
Grand is not the place to go cheap...