"Can anybody tell me specifically what hoops the manufacturer has to go thru to get it certified..."
Depends on the type of part, but generally, you have to test and demonstrate (To some body such as the FAA) that the part is fit for duty.
For some parts, this could mean destructive and non-destructive testing, putting stress on the part (thermal, pressure, tension) and ensuring it will perform as advertised. Then it needs to be tested within the system it will be attached to. A part that seems just fine on its own can start behaving in unintended ways when added to a system (metal incompatibilities, vibrations, etc.).
For avionics, you have to meet a bunch of coding and development standards, on top of the physical things. Put your equipment through vibration, thermal testing and so on, but also ensure that code was developped and testing in a such a way as to ensure no (or very very very few bugs), with things like coverage testing, no unused code, unit testing, and keeping the system highly deterministic and sometimes hard real time.
There is a LOT that goes into certification, hence the costs. Some vendors will make the part that is certified (has the paperwork behind it to supports the fact it was tested and so on) available as uncertified part for a lesser price. but that part without paperwork for proof of certification cannot be installed in a certified aircraft.
For example, Van's sells certified and non-certified Lycomings. EXACT same engine, one with, and one without paperwork, the later being less expensive.
Note that one can follow certification-quality processes, tests, methods, etc. without bothering to PROVE it to the FAA. This is done with experimental parts ... I believe Dynon has stated for instance that they follow much of the same approach as for certified avionics internally, but just don't go the extra step of convincing the FAA that they did ... this can lead to high quality non-certified parts.
Other experimental parts manufacturers don't go that far ... that's what you lose in the experimental world ... you don't have the certainty that whatever you're buying was developed and tested thoroughly, to detailed and very high standards ... maybe they were, maybe they weren't. Good research usually helps you weed out the good from the bad, based on your own opinion and research ...
