I like the Voices.com model where I put a sample script and a range I will pay for the project. The higher I offer the better voices I get. With this I would not hire anyone without seeing a great videography/DP demo reel. Offering between $500-$1500/10 hour day portal to portal, (or basically 8-10 hours of work and you throw in the overnight stay at the lodge) would get you some pretty good samples. You should be able to see the difference between the high and low, as I do with voice samples from voices.com. Sure, some poor shooters will ask for the $1500 but their reel should reveal the quality you will get.
Rich Rubasch
Tilt Media Inc.
Video Production, Post, Studio Sound Stage
Founder/President/Editor/Designer/Animator
https://www.tiltmedia.com