WIFI Based product location system

Hi there, We need an experience and experimenting software engineer (coders please excuse). Project is to develop a utility which identifies location of wifi enabled devices location exactly. There is free source tool available in market. We will need it to get customized as per needs. Please do your research, evaluate your capabilities, before quoting timelines and cost. Off late we have seen alot programmers leaving projects because they could not calculate their hours properly. Happy freelancing. Akhil