They are usually referred to as pins. The configuration is explained on the product info page under the Specifications tab.
You can get 93's pinned to just about any manufacture out there.We use those mics for our other Shure SLX system, but I did not know if they could come with TRS connectors.
The Shure 93's we have use the TA4F connector (if that is what it is called) where it is like the mini-XLR, but with 4 prongs. Why does it need this 4th prong? (if that is the right word.) That has always been something that has confused me a tad.
Really though, for HS kids your best bet is to get the cheaper mics and just budget to replace them every other year. I know that sucks, but if you go out and buy a B3, they will last longer, but I doubt they will last as long as they would in a professional enviorment. HS mics get hairsprayed more often, makeuped more often, and switched off and taped more then anything else. I would much rather lose a 70 dollar mic every show then lose a B3 every show.If you only need to buy one, go for something decent. If you need several, or more than one, instead of buying crap (and that is just what those are), buy one decent one and rent a few. Do that each year. Even if half of the cheap lavs that you could purchase still work next year, they won't last much past that. This way, in a couple of years, you will have a good supply of good mics.
The only time that I recommend renting is when you absolutely have to, and from your budget, I think that you are in that boat.