Recommend software to track our email response time

We want a proposal for three 3rd party software solutions that can track our response time to our customer sales and support inquiries. We have an ecommerce website, and most of our customer email us with sales related questions. Our employees currently use a variety of email clients to read their emails and respond. Customers email a "sales" email which gets read by several different employees. Right now we have no easy way to know how long it takes each employee to respond, or even if they respond. To complete this project, you will understand our requirements in depth, and recommend 3 solutions that are very cost effective and easy to implement with low overhead. The proposed solutions should be inexpensive, easy to set up, and easy for the sales staff to use. Automatic replies that customers receive should be configurable. Although we do get support related emails, most are sales-based, and we want the customer to feel confident they will quickly get a response. You project deliverable will be a document that lists the pros and cons of each solution in detail as it pertains to our business, along with a pricing quote from each of the 3 vendors for 4 salespeople. If possible, we would like to see a demo of the 3 solutions. You do not have to actually implement our choice.