Thinkpads are what you want to look for. You can get a refurbished one from eBay or Amazon Renewed for $300 and they almost all have upgradable storage and RAM, as well as having the rest of the parts being easier to replace than a consumer laptop.

The T14 series is the one to look at.

Onn/Thompson sticks. They also use the stick form factor but they run Google TV so they shouldn’t be affected.