How come iPad Air's price varies on different devices?

How come iPad Air's price varies on different devices? Me and my mom was browsing the new iPad Air on Apple's website on different laptops (we both set the website to US). On my mom's Microsoft laptop and my iPhone 6s+ , it shows $749 for Sky Blue, 256GB Wi-Fi iPad Air. Meanwhile, on my MacBook Air (early 2015), the price for the same product and details is $699.