Don't worry the cost will go down to like 20k very soon.
There are only 8 slots open atm out of 147... I think it's 147 some one correct me please.
So out of the 30ish active clans there will be plenty of slots left over, I reckon maintenance costs will be pretty low. At least this way random banners for long dead clans won't be an issue.
With this people that no longer need a banner won't renew and people that won't one will be able to get one with out lots of faffing about.