Watch for a good used set of Konis - they come up fairly frequently for $100 to $150.
If the bike pogos over bumps, they're really really gone. I experienced that on an old Volvo once - one of the rear shocks must have gone a while before, and then when the other went, it didn't take any bumps at all for the back end to pogo on a completely smooth road. But that's the only time I've had that happen. Usually the ride quality goes to hell way before they completely fail. And I've always heard the stock Boges are pretty poor quality to begin with, so it's a good idea changing them now no matter the condition.