Amazon offers the Bushnell PowerView 12x50mm Super High-Powered Surveillance Binoculars for $35.99 with free shipping. That's the lowest price we could find by $19. They feature a rubber-armored body and Porro prism system.

Note, the 10x50mm and 20x50mm versions are each available for $37.99 with free shipping. That's a low by $20 and $27, respectively.