Simple plugin - PHP distance calculator

Simple web-site plugin for our job site... We have created a list of localities (town and state), with corresponding longitudinal and latitudinal coordinates. Record layout is like "Sydney" "NSW" "151.20682" "-33.86989" (please find sample locality dataset attached). Plugin requirements: Our site visitors will enter their town and state. Plugin will find all job vacancies within a 100 kilometre (62 mile) radius and display them in order of proximity to the town/state entered. This should be fairly quick and easy for anyone who knows their mathematics (trig) and PHP. This project is urgent. Please follow these guidelines when quoting: - Quote your full and final amount. No estimates or hourly rates please. - Outline your understanding of the requirement. Feel free to do this in PM if you like. Please be aware that if your quote simply state something like "we can do this, please give us a go", it will be ignored. We will pay in full upon completion. If you require clarification, please post any questions in PM. Thank you, and good luck!