I mean, Engine Oil and Spark Plug you can pretty much use universal brand. I know the transmission oil is special. I bought 4 qt at $34 in dealer today. What else are special on Prius? I quoted the accessory battery, the price is $145. I think that's a total rip off. Thanks!
When the time comes for you to replace the spark plugs, I recommend that you stay with the original equipment Denso or NGK iridium spark plugs, specified in the owner's manual. That plug type is specifically designed for 120K mile service life, which would not be the case with a "universal" plug. The engine and inverter coolant is Toyota Super Long Life Coolant, which costs ~$21 per gallon, premixed with distilled water. I don't recommend that you cheap out by buying generic coolant for $8 per gallon, as the financial impact of a clogged system will be high. The air conditioning compressor oil is special and is electrically non-conductive. If you use the wrong oil that will cause a high voltage ground fault and the compressor (and other AC parts) will need to be replaced. If you can find another 12V battery that has ~35 Ah capacity, fits within the available space, has the correct terminal polarity (so that the positive terminal is to the left, as you are facing the battery with the terminals closest to you), and uses absorbed glass mat design (so the battery won't leak acid everywhere if your right-rear fender is hit in an accident) for less than $145, go for it. Good luck.
Other than the 12V battery and the A/C compressor oil all other maintenance parts or run of the mill Toyota stuff. Personally I would just stick with Toyota materials (other than motor oil and filters) just to be sure that it does meet OEM spec though.
