I think it's $9 or $10 per day and if you keep your stub you can use the other theme park parking for free after that as long as you show your stub from your parking ticket.

Just a note to say if you are staying at a Disney hotel, and using a hire car, parking at the Disney parks is free.

Another way to get free parking is for one of your party to get an annual pass rather than the usual MYW or 7/14 day passes. The annual passs gives alsorts of other benefits/discounts too). The AP has to be bought direct from the U.S. (they have them on the WDW website). They are particularly good of course, if you happen to go twice within a 12 month period !!!