I can't seem to find this info on the internet- how much exercise should a Border terrier have in general?

Overall Exercise
100 - 120 minutes per day.

The Border Terrier is a very active dog, bred to follow the hunt and with keen hunting instincts. They need plenty of exercise on a daily basis and enjoy using their intellect as well as their bodies. They have lots of stamina and will keep going as long as their owners require them to do so. They may chase any small creature that take their fancy regardless of life and limb. This can lead them into trouble but an owner who is aware of this and starts appropriate training at an early age should remain in command.

Hope that helps! :)

Obviou7sly guest we are talking of adult dogs here :D

My Borders are happy with 40 mins to 1hr each day, they thrive on human company so being with you will what the dog requires the most.  I can work mine for upto 6/7hrs continuously doing certain things, so they will take as much as you give.
Dawn.