I recommend the YYF ONE. At $10 US, it’s very inexpensive. Order it in multiple colors and just order the package with 2 bearings. As students advance, you can swap out the installed responsive bearing for the full width C bearing and make it unresponsive. This is where most of the yoyos you buy should be. You can download the contents of the DVD off the YoYoFactory YouTube channel if you want it.
Also, order a bearing puller, but I recommend a YYF multi-tool instead. This has a bearing puller and a string cutter. Maybe 2.
For looping, again, going with lowest cost, the Shinwoo Loop is the same price. but loopers don’t need bearings to be swapped out. I’d say don’t order more than 5 of these at most. Most people are into the 1A stuff.
Also, just to have handy, order a couple of YYF WHIP’s. At the same price as the ONE, they are fun. The only downside is they are unresponsive. See if you can get extra budget for this.
Get a tube of both YYJ Thick and thin lube.
Lastly, order either 1 or 2 100-counts of either the YYE Slick 6 or 100% poly(or one of each). White is fine, but other colors re cool too. The neon green is a nice choice.
If the kids are into it after that, it’s time for them to order their own!
I own a ONE, a WHIP and got a LOOP for one of my kids. I may come back and order another LOOP for myself. Fun stuff, good stuff.
After that, it just doesn’t make much sense to provide more or better. I’m not recommending low priced junk, these just happen to be inexpensive and well suited for your environment.