Ask HN: Offering conference attendance packages to employees

The company I work for is considering offering once per year conference attendance as a perk and we're trying to come up with some ballpark estimates for how much this might cost. We're not sure exactly how much of the event and associated costs we should cover though. I'm hoping some of you can point out some industry norms.

Those of you who have attended a tech conference on your company, how much of the overall cost did they cover?

Tickets? Travel? Hotel? Food & discretionary? Other?