They have quota controls as well. A soft limit that will send you alerts when you hit them and you pay 1.5 cents per search and a hard limit that will stop searches from being run.
Personally I went to a tier that I dont exceed (10/month). I ahve considered going to the annual subscription which is also unlimited but the same as the 25/month, just discounted a bit. I could probably write that one off for work too, definately could with taxes.