About $27 is the highest (at my current registrar, few $ less if I moved it) but it is a name I don't plan to renew partly due to cost; the highest that I plan to pay / have ever paid is about $15.
I often try to find specials on multi-year registrations in advance at good prices. My average ngTLD renewal cost per domain is well under $8, and I mainly renew only those with some indication of interest or that I see a trend that will be much stronger in the future.
Thanks for starting thread,
@Arpit131