Not to mention the more you produce, the faster the tooling wears outs and the sooner you have to replace. I know peopel will look at it and think “plastic, causing metal to wear out?” Well, yes, it does. Then there’s the question of how bad do you let it get (reducing quality of the final product) before you spring for fresh dies.
One other thing, people take today’s money and look in 30-40 year old magazines and think that the hobby was so much cheaper. You also need to look at inflation as well. This has never really been a poor man’s hobby, even going back to the early days. When the first electric trains came out - electricity in your house was a luxury, not everyone could even afford to have electric lights, let alone an electric ‘toy’. Sure, there have always been ways to scrimp and make due with available materials (empty tin can stock and so forth), but if you look at the fully ‘finished’ layout even 50-60 years ago, notice how many of the people buildign them were doctors and other such professions. Not too many Joe the Plumbers with fully finished 50x30 basement empires full of highly detailed locos and perfectly accurate rolling stock and all craftsman-level structures. Then there’s the time vs money trade off. You can have more for less money if you have more time, or you can have more of a layout in less time if you have more money. So maybe you’ve found a way to make that othersise unafforable dream layotu a reality - but if it takes 100 hours to build that highly detailed insid