Well, the Seed Signer project claims that components required to build the device usually costs less than $50. The catch is you have to build it yourself, which could be a good thing because you can verify the build yourself. You are also sourcing off the shelf parts, which means it's less obvious than having a Jade or any other high profile hardware wallet ship to your house.

That said, I have no personal experience with the Jade or the Seed Signer. I'm a Coldcard guy myself. So, my comments probably don't mean much anyways...