[gregr401]

Expensive for whom, how exactly do you quantify that? Today we pay fee's to institutions which have massive infrastructure costs (along with their necessary profits). If anything, decentralization offers an incentive for the technically inclined to reap some potential rewards which is far more feasible than today's systems.

[wmf]

If you don't think decentralization is needed then Ripple is just as good as Bitcoin but it requires no mining. So the expense is the wordwide cost of all Bitcoin mining which is estimated at over $100M/year.