Howdy!
I'm an Austin, Texas based PHP developer with 12 years of full-stack programming experience. I just completed a project for a client using Google's Distance-Matrix API, which sounds like it would be well suited for this as well. The alternative would be a zip-radius implementation, far more complex, that would add an additional $100 to my bid. All depends on how many entries you have to get distances for and how many visitors you have.
Would love to chat.
Regards,
Joseph Cardwell