Logical bug: If any product is bought by Buy/Sell menu, it is obtained faster and even cheaper, than to use tens of paid workers to manufacture it.

Example: direct buy of Plasma Rifle costs 2500 c and it is immediately available. Production of Plasma Rifle will cost also 2500 c, but takes production time (23h in my situation) and also consumes 30 pcs alien materials.
The same is for all products incl. standard Earth items, like weapons or aircrafts. Buying them is both cheaper and faster than manufacturing it, because wages of workers must be paid.

It is logical to have some costs to manufacture items, but these financial costs cannot be 100% of the standard purchasing price of that item (in original UFO series initial costs to manufacture items is 0). I would recommend initial costs for example 25% of market price of the manufactured product, paid immediately when production starts. Income from manufacturing and selling items (margin) must be able easily cover expenditures for workers wage.