Extension of Local Area Network

I have a Local Area Network of 98 data point with one sever running WIN2000 sever OS, Exchange and proxvy. Our LAN is scatered around all Hospital Campus, We have very/tight budget to spend on LAN BUt we need to add up a new building which is about250mts away from the server What cheapest and reliable technology should I use, please advice “on your advice consider we are located at developing countries“