Following up is trickier than backpedaling out of an awkward family argument. "No Mom! I NEVER liked your grilled cheese sandwiches... well I liked the ones you made before you divorced Daddy... why are you crying?"
Back to business... so have you ever made a connection with a possible client, they're all excited to work with you, you send them an estimate, then it's radio silence? Yup. Welcome to the creative freelancer's club.
Ideally give it a week after you sent them the estimate for them to mull it over and speak to everyone involved if it's a bigger client. Then write them the following script. If you still haven't heard back from them after that then it's time to move on. If they didn't hire you for this specific job please remember they will have you in the backs of their minds for upcoming jobs in the future. Use the time between now and then to reach out to more dream clients.
FYI: Use this script with caution because each instance, client, and creative freelance job varies dramatically. So above all else, make this script work for you and your exact experience with the person you are writing it to.