Thanks for reaching out. I hope your Monday is going well.
At this time, this feature is unavailable to use on estimates. However, if you'd like, I can submit feedback to our product developers so this could be considered in a future update. In the meantime, I recommend checking out: Use Advanced Pricing for more details about using the quantity discount feature.
Please don't hesitate to let me know if you find you have further questions or concerns. I'll be sure to keep a lookout for your response. You can always reach out to the Community or me anytime you need help. Take care and have a great week ahead!