Hope this makes sense

I am looking for methods to remotely access computers to perform repairs. I have only been on the receiving end of this and have used Lan Desk, and Webex. With Webex I had to go to a URL then the support person could take over the computer and no software had to be installed on the users computer. I have no idea what Webex costs but I bet it's not cheap. Is there anything free / cheap that works the same way ? I am looking for something where the user doesn't need to install something on their computer ahead of time.