Ok, let's ignore the costs and look at the risks.
Burial in a non-tectonically active site - chances of an earthquake? Say, once in in 10,000 years +/- 2,000 years.
Blasting into space? Let's say the age of rockets is 50 years old. How many catastrophic failures have we had in that time? (I can think of two shuttles alone in the last twenty years).
Failure of a rocket transporting nuclear waste into space would cover the entire Earth in a nice, even layer of radioactive debris. And how often could we expect that to happen? If transported by Shuttle at the same mission rate, about every 13 years +/- 3 years. These odds would shorten though, if there were more frequent flights to export our nuclear waste.
Hmmm, think I know what I'd prefer.......