I did a bit of research to build a comparison for my boss. Here is what I cam up with. Hope it helps others out.
Mapbox and Mapquest are cheaper than Google, but Bing, HERE and Tom Tom appear to be considerably cheaper.
Example of 400,000 calls per month:
Google already built into extension)
28,000 free then $7 per 1,000.
$2,604 per month
Mapbox (already built into extension)
50,000 per month free then a sliding scale.
$1,250 per month
Mapquest (already built in to extension)
15,000 free then a tier system. Up to 500,000
$799 per month
Bing Maps (already built in to extension)
125,000 per YEAR so only 4,167 per month, then half a cent to 1.5 cents per transaction based on volume. I used $0.01 for this calculation.
$399 per month
Tom Tom
75,000 per month free, then $0.48 per 1,000
$156 per month
HERE
250,000 per month free, then $1 per thousand
$150 per month
Here has a pro level that is $449 per month and allows 1 million transactions per month plus extras.