All helmet testing is debatable, including the much respected (but probably pretty good) VT testing. The "official" safety standards are similarly debatable.

I have a couple of inexpensive (~$50) Bell helmets I purchased in years past that have MIPS, are comfortable and ventilate well. I also have some expensive helmets (Kask Utopia, POC Tectal Race Spin, Bell Z20) that are the ones I actually wear. These helmets vary between $200-$300. From a pure value perspective, are they "worth" the money over the $50 helmets? I'd say no, but that never stopped me before when it comes to bike stuff. Aero carbon frames cost a ton of money and offer only highly debatable performance benefits, the same goes for carbon wheels, Dura Ace vs Ultegra etc. Similarly, the nicer helmets are better made and can be more attractive, but they're likely not really "better" functioning in any appreciable way. The Kask and the POC don't even have MIPS...

If you're only looking for functionality, just get an inexpensive, certified helmet with MIPS that fits you well and move on. I would not buy used helmets. I also don't believe that helmet's "degrade" over a few years, especially if you store them out of the sun. You probably don't want to wear a 20 year old helmet, but that's obvious.