I had a Seiko SQ which I picked up from ebay as a non-runner for £5. Since purchase I spent further on finding the right bracelet for it- lots of experimentation there- batteries and getting it cleaned properly. So over 4 years or so, only £100 more I would guess, £150 tops.
And then I sold it for £50. Small beer perhaps but when you think in % terms....
I was never much good at investment.