Even if you go through a consolidator to get airline tickets to Africa, prices can range from $2,200 to $2,600 — and that's on the low end for someone traveling out of Salt Lake City. Generally it's best to book your tickets as far in advance as you can.
For a safari destination like the Masai Mara, the cost to stay in the park can be $400 to $500 a day. The flight to the park from Nairobi is about $300. Be warned, you can only bring a 22-pound bag on the flight to the park (a bit of a challenge if you carry a lot of camera gear).
We booked our safari trip with a Kenyan company, Tawasal Tours and Safari.
While you can use a Visa to pay for your room and meals, it's recommended you carry at least $200 in cash. American dollars will work in most situations, but I'd recommend you also have some shillings, the currency of Kenya. At the end of your safari, it's traditional to give your driver a tip, about $40 per person in your vehicle.
As for souvenirs, I'd suggest shopping in Nairobi. The Masai Mara lodge has a gift shop, but prices there are high and you can't bargain.
Lastly, photography. Bring a camera with a telephoto lens. Although the animals are most active in the early morning and late evening, the light is generally good enough at those times that you can shoot with a lens that has a higher f-stop. I took a 70-200 Cannon lens, f/2.8.
If you stay at the Masai Mara lodge, your tent should have an electrical outlet so you can charge batteries for a digital camera. Some people in my group brought a laptop to download photos. I brought a portable download device called an EPSON P-2000. It's about 4 inches wide, 3 inches tall, 1 inch thick and will hold over 36GB worth of photos.