Had some crazy mold in my car after it sat for a while. Been going through a few different methods of cleaning.
1 Soap and water. Should be used to remove the surface mold first and foremost.
2 Bleach and water. Pretty useless. It WILL kill mold, but not all kinds of mold, and smells gross. Dont bother with this option.
3 Water and Tea Tree Oil. It works, but unless you really get enough to penetrate all materials, its not that useful, and smells horrid. The smell does air out within a couple days.
4 Water and borax. Works good. Natural antifungal/insecticide, it raises the moisture ph to 9-9.5 and I suppose makes it inhospitable for wee organisims to live. On top of that, its a decent de-ordorizer as well. Just used this yesterday, so not sure if it works in the long run.
5 water and vinegar. Supposedly works, but the smell is not worth it!
6 Moldex Spray (Crappy tire is where I got mine.) This seems to just be a mix of perfumes, Isopropyl Alcohol (5% by volume) and a 6-7 word chemical name which I could barely read, never the less type or say (.97% i believe.) This stuff really left a nice smell in my car, it appeared to have worked to take out what was there. I soaked the areas, let it dry, vacuumed, repeat.
7 SUNLIGHT AND AIR! After cleaning, recleaning, and then cleaning again, when you can, get a good dose of sunlight on there and keep em dry.
I know a general idea is when there is a bad colony of mold, to just toss it, and thats a nice idea, but not everyone can afford that. I would LOVE to rip the seats and carpet out of my car, but spending 800 odd dollars for new everything isnt a realistic option. And considering your vests are worth 500 dollars, I wouldnt want to toss em either! If I were you, Id go with the soap, borax, moldex options. Clean one day, let them dry for 2. If you can get sun on them, all the better. Clean with another item another day (Id say soap, then moldex, then borax) and let them sit again. If after cleaning, then letting them really dry for a couple weeks they still have signs or smells of mold, then toss them. If it smells alright, and you dont get sick from wearing one, 500 bucks saved!