As a manufacturer of these things I can answer this question quite easily.
The simple answer: Make one and see how much it costs you in parts, labor, R&D, premises, machinery and test equipment, certification costs, taxes and duties, electricity and other municipal costs - then after all that add a bit if you don't feel like making this for free, then start dealing with shipping costs, insurance and distributors (which likely will simply double your price to them, if not even more) and you'll soon see that these things are actually not that bad.
In the end the manufacturer only gets a tiny fraction of what you spend to keep as profit. You are looking at perhaps 2-5% tops.
Economy of scale comes into this of course. If you produce a batch of 100 or a a batch of 10000 makes a huge difference in many ways.
We work on 1000 units just to pay off the certification costs (and that is just FCC). So you see you need to take a bit of a long term view on this and hope that your product is not going to be obsolete before you recouped all costs involved in developing it.
Then you have the added huge hassle of securing your supply chains - right now international electronics component supplies are under very serious strain and it can be hugely difficult to even find basic components like ceramic capacitors. If you do - be prepared to pay premium prices. Currently we get quoted lead times into the year 2021 for some components.
You can imagine what that means for any electronics manufacturer.
We are even affected by the U.S. - China tariff war. We source many of our components in the U.S. and have to pay U.S. tariffs of up to 25% on many of these items and even risk double tariffs these same components enter the U.S. again. It's a mess.
Bottom line - don't complain about the prices. They are really not bad for what is involved...
Rainier
CEO MGL Avionics