Hello again everyone

I have a 2004 Accord EX 4 cylinder automatic.
I cant get it thru inspection because of an evap code and a knock sensor code. Went to a local mechanic and was disappointed at some of the prices he was charging. For instance he wanted $300 to replace the passenger side mirror, which costs about $50 to buy. Even if he doubled the price of the part, I know that doesn't take 2 hrs of labor for a professional to replace. I'm gonna try to do that myself.

Anyway, as far as getting started with some of the other repairs he agreed to let me purchase the parts myself - the knock sensor and some air intake thing - and bring them to him, but saying that he couldn't guarantee the parts of course in case I bought cheap parts.

I've been googling around and I see these knock sensors running from around $14 to close to $200. It has dawned on me that I have no idea what I'm buying.

Can anyone suggest a reputable website or place where I might be able to find what I need? Maybe even with a little assistance?

Carparts.com has sales agents, one of whom was advising me on a side mirror. I don't know if they're reputable or really who to trust regarding the quality of the parts when it comes to something that I think works with the engine (the knock sensor).

What about actual stores like Auto Zone or Advance? Is that bad?

Thanks for reading
And TIA for any advice you may have