I am wondering what is the best way to get a set of Lego bricks for my kindergarten classroom? The children love playing with them and I no longer own them due to a transfer of grade levels.
If there is no need for the bricks to belong to specific sets (as in, it's not important to be able to build some official models from them) then I'd say the best way is to look for ebay bulk brick sales. For around 100$ you can get several pounds or around a thousand semi-random pieces. Try searching for "lego pieces".
You have a lot of resources at hand as a teacher in your community. Have you considered sending home a request for gently used LEGO Bricks in your student's folders at the start of the year?
The parents of your kids may not have any on hand, but will certainly know someone who does!