In most cases, yes - you're able to beat your rental car Price to Beat by using your own/friend/family car instead. However some companies do not validate driving instead of flying. You should check with your team to make sure you will be eligible for points!
We do ask that you forward your gas & toll receipts as well as mileage to Rocketrip. These costs will count against your rental car Price to Beat. Please reach out to us at firstname.lastname@example.org if you plan on using your own car or a company car instead of renting a car for your future business travels.