I got a used Surface Pro earlier this year for exactly this purpose. It was the previous gen at the time - Surface Pro 4, instead of the newer 2017 Surface Pro

I got a used Surface Pro earlier this year for exactly this purpose. It was the previous gen at the time - Surface Pro 4, instead of the newer 2017 Surface Pro. It looks the same as the 2017 model and the new SP6, though. Since I mostly wanted it for PDF reading, I got the low end one with a core m3, 4GB of RAM, and a 128GB SSD. It cost about $400 (Canadian) on eBay, and came with a Surface Pen. If you don't mind buying something pre-owned, it might be worth a look. There seem to be lots of them on eBay that were leased by companies and then used very gently. The one I got looked like new and even came in the original box.