For a personalized plate you pay the regular registration fee for a normal plate ($20 for two years) plus an additional $50 (again, that covers two years). There's also a one-time charge of $11.50 in handling fees, etc.
However, if you are replacing a current plate, you do get credit for the unused portion of that plate's registration. I still had a few months left on my old registration sticker, so my total for the personalized plate was about $75.
In short, I'm paying an extra $25 a year and also a one-time fee of $11.50. That doesn't seem like too much, considering how much the plate beautifies my car.
I requested the plate and sent in the fee in late August and got the plate in late October.