I used to live in Kenya and have travelled a lot around Southern and East Africa and my tuppenceworth is that it could be all things mentioned so far. It can also be very unethical. Google Ritz Carlton Masai Mara, for example and please do not stay there.
For the best experience, I would suggest a less visited part of the world than Mara or Serengeti. Samburu, in Northern Kenya would be my top choice, as well as Ol Pajeta which you could combine on the same trip.
f you can not afford a lodge, take a tent and rent a car. There are public campsites in every park. The ones in South Africa are particularly good. You can always go to a lodge for lunch and a swim during then hottest part of the day.
Last thing, I would really encourage you to use a local, ethical company to keep the money flowing into the places that need it.