So what do you work on that you can't buy parts for??
Do you do machining as hobby ... umm ... for fun

, or do you do machining because it's PRACTICAL?
The oldest thing I had to fix up was 1950's forklift. I THOUGHT I'd have to get some parts custom made, but actually was able to buy everything I needed either as direct replacement or adapt from other automotvie applications (starter, hydraulics, brakes master cylinder, etc).
Typical automotive jobs I've been bringing to machine shop - resurfacing cylinder heads, turning brake rotors, valve grinding - were all under a $100. For cylinder heads it might be a bit over a $100 depends on the shop.
How much $$$'s worth is in climate controlled shop space that is being used up by the lathe/mill/surface grinder, tooling and metal stock? I figure it would be a hundred bucks a month or more. And that's just fixed cost, month after month regardless if machining equipment gets used or not. Some choose to ignore that cost, because it's indirect - but dry, accessible, heated/air conditioned floor space is rarely truly free.
For cheap equipment - typically it's cheap equipment that needed repairs, parts and additional tooling = time and money. More importantly what's the total cost of having equipment setup and working in your shop? So you buy a 14 ft gear head lathe with a 20" chuck for $500, but what's your total cost with rigging, moving and setup included?
Do you keep track of how much time you spend machining parts and how much $$$ your end product is worth vs how much $$$ your time is worth?