Two events with configured PRICE - Price option is only showing on one
Found it. The option "approval required" breaks the price option.

When that option is checked, the price options are not printed on the registration page. No idea why this behaviour is standard though.

My client needs to check this option AND needs to ask about price option, so in the current civi-logic (this is becoming a peculiar word, civi-logic) he needs to add a price field in the used profile instead?