I would put 10k at the very top end of the price range for SuperNats. Most teams I talked to were between 3-5k for a SuperNats arrive-and-drive in X30. 5k for a WKA weekend sounds insane. You could rent an engine and kart for like 1k for most national races. If you want to get under a tent program, I can see that price going up a little, but 5k is someone putting quite a few bills directly into their pocket at your expense.
I won’t disagree that karting can be costly compared to some of the lower level formula series. Arguably, karting DOES provide better competition and much more intense racing. I suppose it depends on what you’re looking for.