Updating Repeated CiviEvents in 4.7 and 5.0
I can assure you that custom fields never carried over to repeating events in Civi 4.6 - I had to write a lot of custom code to deal with the fact!

The issue you're describing is CRM-16902.  It's marked as closed, but that's incorrect - a related issue, CRM-20787 was recently fixed.

Before CRM-20787 was merged, it WAS possible to change a single price on a repeating event.  This might be the changed behavior your client is noticing.  If selecting "this event only" isn't possible now, that's a regression and should be reported.

That said - dealing with price changes and price sets is very thorny.  If I change event 3 (only) to have a different price, then I change a different event's price and say "change all events" - does event 3 have the new price?  Or just the unchanged events?

In short - it's not a quick fix.  It needs code to be written.