Here in Victoria, Australia, a custom plate costs $500 AUD, that's $395 USD. At least you don't have to pay for it every year.
If you want just 3 numbers (e.g. 986) or two letters (e.g. FP), the price is around $1000. If you can get one. I saw the plate 239 auctioned a few weeks ago for $70,000.
And did I mention we can be fined for doing 3kmh over the limit?
Registering a sportscar here is akin to cruelty. Luckily they can't police all the roads all of the time ;-)
Anyway, I've been looking at the authority's website to register one, which has rules to prevent you registering plates that might be offensive.
So...
You can't have BLK-BOX or LRG-COK
But you can have SML-COK
Funny that.