I would be following the AJAX route as you have tried, creating a new controller action and set the AJAX to fire off of a client side timer.
private string _FolderPath = Server.MapPath("your filepath here");
private System.IO.SearchOption _SrcOpt = System.IO.SearchOption.TopDirectoryOnly;
public JsonResult GetFileCountJSON() {
int filecount = Directory.GetFiles(_FolderPath, "*", _SrcOpt).Length;
object ReturnData = new { "FileCount", filecount };
return Json(ReturnData, JsonRequestBehavior.AllowGet);
}