Apple now allows educational institutions to purchase Apps in bulk at 50 percent off the regular price.
In order to make these volume purchases, institutions must obtain vouchers through their Apple Online Authorized Purchaser. The vouchers can be purchased in amounts of $100, $500, $1,000, $5,000 and $10,000.
Here is Apple's description of the program:
The Volume Purchase Program makes it easy for educational institutions to purchase iOS apps in volume and distribute those apps to users. The Volume Purchase Program also allows app developers to offer special pricing for purchases of 20 apps or more.