Hi Jennie & Denise
I did the Kenya trip last September, the same one as Jaya actually, and absolutely loved it. It exceeded all of my expectations and I am seriously thinking of going again.
With regard to what money to take, I agree with all Paula has told you i.e. no more than £250 in Kenyan shillings. There is not much opportunity for shopping only the roadside stops en-route, which usually consist of one shop or stall, and the hotel gift shops which are nice to look round but don't have an awful lot. Otherwise all you need is cash for drinks etc.
There are ATMs at most of the lodges if you do run short and I would suggest a currency card is a good idea as you will then have it for future holidays as well.
Have a wonderful holiday, from the moment you arrive in Nairobi and meet the jeep drivers you will know you're in for a great time.
Best Wishes
Sue