It was free!

Because the 5 yr registration is pro-rated at $10/yr for a 5 yr period they take into account how long it has been sense you registered for the standard plates. Because of this fact I essentially had $32 of remaining 'balance' on my standard plates and 3 yrs ($30) until I have to re-register my new antique plates. So I guess if I wanted to get technical they should have refunded me $2.