CamBam CNC Software
cambam is low cost and would most likely suite the needs for high school students . Lots of hobbyists use it and have good success with it
its not high end like mastercam and such , but its cheap for what it does , and it wouldn't surprise me if you'd be able to work out a package deal .
bobcads ok and works ok but its hard to say if you'd get that many seats within your budget , and if you cant get the 3d milling then don't bother with it , bobcads a bit tragic and limited with 2d in my opinion , at least thats what i found in v23 , v24 may be better
your only other bet would probably be dolphin cam