2003 Honda Odyssey Key will not turnin the ignition

At first it was just difficulty inserting the key in the ignition but now the key inserts but will not turn. We have tryed graphite spray, the valet key that has very little use - now we just leave the key inserted and tell everyone - do not remove the key!

A mechanic told us that the dealer would have to do the repair and it would be expensive!

Any ideas?

Thank you.