The Surface Pro 3 shares a trait with many mobile devices these days: it's designed so it cannot be upgraded. With no visible screws, Microsoft clearly intended for this tablet's specs to stay the same from the day it leaves the factory to the day it dies.
But what Microsoft probably didn't take into account is that some engineers would take the limitations as a challenge, and not a restriction.
It turns out that there is a way to upgrade the Surface Pro 3. if you happen to have a drill press, a Dremel, and casual disregard for the risks you're running with a thousand dollar tablet, you can choose to upgrade the storage on this tablet.
After growing dissatisfied with the mere 256GB of storage in his tablet, one Surface owner in Mexico set out to fix the problem. His solution: use a Dremel to mill out a plate from the rear of his tablet and then remove and replace the SSD with a higher volume unit.
He bought the 1TB drive online for $400, and that was the easy step. Getting that drive into the tablet involved first identifying where the SSD drive was located and then cutting away the shell which covered it.
The SSD can be found under the kickstand, which is convenient. Since that component is largely useless, there's no problem with leaving it folded up and covering the hole.
This next picture is not for the faint of heart:
The SSD was held in by a couple screws. Once he had it out, the madman cloned the old drive to the new one, and then inserted the new drive into the tablet.
He says it boots, and works just as well as it did before.
Theoretically, one could buy the cheapest Surface Pro 3 model (with 64GB storage) and upgrade it. That would save around $600 at the prices this guy paid, but i think your money would be better spent on buying a tablet with the desired amount of storage elsewhere. That would save you from paying Microsoft's premium for their flagship tablet, and it would also save your warranty.