comparing connection speeds and costs

Where can I learn more about the associated speeds and costs (average) of the different types of connections? I need to determine feasibility of the faster connections but still base it on cost. We currently use cable and are pretty satisfied with it. Most vendors I have spoken to tell me that if we are happy with our current connection speed, we should stick with it due to it’s relatively low cost. I would like to find an article that also confirms that statement. Any ideas?