Server -> Client problem

I'm currently developing an application that will in essence keep the client in a constant stream with what the server is aware of.

Now, I don't want to use sockets as I don't fancy using a shit-tonne of servers for a relatively low amount of data transferring.

So, I'm trying to take an approach that will use SQL as well as possibly an AJAX script that will constantly update the html so the connecting devices can keep withdrawing that information without having constantly URL requests for data. However, I'm expecting this to be a whole lot more problematic that I'm anticipating.

The data presented will be simple chat logs, as well as a certain data for a url request for the client. However, I want to keep each device in sync with each other give or take a few seconds. The problem becomes where the server will know where it is at. Without client feedback for updating the database or whatever.

I'm not asking for an in-depth analysis of the server->client way of doing this, I'm asking if there are any better ways of doing it for keeping bandwidth low & requests at a minimum?