Personally I'd wait. Most Attakus statues can be found far below their suggested retail price after they've been released. The latest two Attakus releases are perfect examples:
Tusken Raider's MSRP= $389 vs. average eBay price= $305
Wicket's MSRP= $279 vs. average eBay price= $215
As cool as the Grievous piece is I don't think the character is so popular that that supply will be an issue either. Especially considering his MSRP ($580) is considerably higher than the average Attakus statue. Just my opinion though.