Chance Google Maps with Openstreet maps for displaying a real estate properties

So people, its fairly simple. I will be buying a website developed in PHP ([login to view URL]). That is the website for searching real estate properties using a map, and that script uses Google Maps from showing properties on the map. I dont want to use that, instead i want to use OpenStreet maps, so i need help. Check out [login to view URL] and go to "Live Preview" to see the script in action... Plz, contact me only if you are 100% that you can do it... Im student, so im on pretty tight budget :D Also, use the word "map" in your bid so i know u read everything :)