Unless the 3 enclosure are exactly the same size and heated by exactly the same type of heating element you are going to have a hard time finding one that will control all 3 for $80. In order to control multiple enclosures they need to be exactly the same or you will have different temps in each one.

Unless of course you use a Herpstat...http://spyderrobotics.com/products/herpstatpro.html

But they are more than $80.

So are the 3 enclosures the same or different? If they are the same you would have more options...