They are either very cheap components, but you paid a massive r&d grant to have them designed for you, or they are very expensive components but you paid no r&d costs.
Choose whatever suits to best avoid taxes, quotas, fees, and regulations...
Not if you’ve valued them very differently before in different tax jurisdictions. There’s definitely a certain degree of freedom in how the components of a finished product are valued when they have no, or very limited, alternative uses, but you can’t just pick a number arbitrarily out of a hat. Companies have to do internal cost accounting to figure out whether manufacturing a component to a certain quality, or in a certain place makes sense, and while there may not be exact equivalents on the open market there will be close ones in most cases. Worst comes to worst you can see how much an order of size X would cost from a manufacturer capable of producing the component. There are many degrees of freedom in transfer pricing but they’re finite.
You can't say "this part is only worth $10" if it's costing you $100 to produce.
Line item on the PO or wrap it into the part costs.
You could definitely hide a lot of R&D within some form of limit, but it isn't a free pass for everything. At least from what I knew in the old UK's standard. There is a new what's labeled as UK's GAAP which I have no idea about.