Years ago, when I was short of money, I sold my lovely Hohner Jack to a friend for £75. I really regret it now as it was a super bass. I tried to buy one a few years ago on eBay but the sale fell through. It only reached £180 which is a really good price as well so it irks me even more that they go for so much now. Don't think I could justify a replacement at the moment.
About 10 years ago, again short for money, and frustrated at my lack of progress with it, I sold an Aria Pro II Cat fretless to a friend for £100 (much better) but I'm now regretting this as well as I'm wanting to try fretless again. Neither bass has really been replaced, but my Fender MIA jazz does pretty well tick all my fretted bass boxes so I can't complain. Still looking out for something to scratch that fretless itch, though, but I think I might go for fret lines instead of a plain neck this time ...