I'm a machinist by trade, with it comes a very odd and specialized field of tools. You either pay through the nose for new, or acquire good used tools as you go. My first machinist tool purchase was a Lufkin #514 0-6" depth micrometer at a yard sale for $2, that I frankly had no clue how to use, but I had seen in the toolbox of all my coworkers. Now, I use that thing 3-4 days a week, been in the trade 7 years, probably the best $2 I've ever spent. Also started my Lufkin addiction.
Another example is inside diameter tubular micrometer sets. I bought a Lufkin #6801D 1.5-32" set off the bay for $100. The modern Starrett equivalent set, 823fz, goes for about $500 on up based on a quick googling. I did have about 2 hours into calibrating all the extensions, but Lufkin mics are some of the best in terms of quality, and hold adjustments very well. I feel they're a bargain on the used market, but haven't been made since the late 60s, so you have to be choosy and find nice, well cared for examples.
That I.D. mic set sat in my work box for 8 months after I calibrated it without being touched. Then out of the blue, started finding uses for it everywhere.
I go with the Boy Scout motto on this one, be prepared.
