I bought 2 M13s (one black, one beige, the one with the builtin track point) in Seattle thrift stores in the early 2000's, one was $5 and one was $10.

At one point, other copies were both $300 plus on ebay.

Sadly the black one has an intermittent issue with some of the keys where hits are doubled, but the beige one is still a daily driver.