I don't know that a Fatar would be the wisest decision. They do make great assemblies for other manufacturers but are know for corner cutting on their namebrand line. While the K25XS is pricey, asdide form the sound and processing power, there's an abundance of control features that makes it worth the cost.
Also, Kurzweil does have an 88 key "stage performance piano" called the SP88. Guitar Center in Atlanta is selling these new for $699.99. Other than what I've read in the GC flier, I don't have any personal knowledge with the SP so I can't say if it offers as many control options. At that price, it may be worth looking at though.