For independent travellers staying outside the reserve, count on paying around US$150 to US$200 per day for a 4WD with a driver-guide and (usually) a picnic lunch. This fee can, of course, be split between as many people as can be comfortably squeezed into the vehicle. There’s no public transport within the park.
Several private operators collaborate with the government to provide four wheelers for driving within the park. For commuting within the park, there are jeeps and vans available, but not buses.
Always prefer a chauffeur-driven vehicle and in the company of a guide who is aware of the roadmap within the park. Also, make sure that the vehicle you are in has emergency safety gear and extra tyre, etc. The only chance for walking on foot within the park is when you are accompanied by armed rangers or, better, by Masai people who are expert at handling the animals. They carry trumpets to scare away the animals. However, even then it is best to be in a closed safari.