Hello Sullen,
Welcome to Microsoft Community.
May I offer a friendly reminder that Microsoft's official sales channels no longer carry the Surface Pro 3 and Surface Pro 4, as both models have been discontinued.
That's why you won't find prices for these two models on the Microsoft website. These two models may still be in stock on the second-hand market or on Amazon, but the selling price may not be the same as the original price of Microsoft. But let me tell you that if you do buy a device with one of these two models, Microsoft will not provide a warranty, because both models have been discontinued and out-of-warranty support and service is no longer available.
Instead of buying these two older models, I actually recommend you check out the Surface Pro 11. As the latest release of the Surface Pro series of devices, it has far more performance than the Surface Pro 4, fully able to meet your daily needs to watch movies or listen to music. However, this is a Surface with Windows ARM, I am worried that you may encounter some software or driver compatibility issues in daily use:
Windows Arm-based PCs FAQ - Microsoft Support
If you are not interested in playing games, then maybe the more compact Surface Go 4 is a good choice:
Buy Surface Go 4 for Business - See Specs, Ports, Price | Microsoft Store****
Or you can try to find the device that best suits your needs by following the instructions linked below:
Let us help you choose the right Surface laptop, computer or PC | Microsoft Surface
Best Regards,
Mitchell | Microsoft Community Support Specialist