It is expensive I'm afraid.
I think the minimum it is worth spending in the Serengeti/Ngorongora is 2 nights on the crater rim (the only way you can spend a full day in the crater) and two nights in the Serengeti (this is assuming you exit west). This comes to a minimum of $1000 for a car and two people. I'd recommend you spend an extra $20pppn in the Serengeti for a private campsite - better to pay $50pppn for something great than $30pppn for something crap in my view. You can't camp just outside other than at the far western end (Serengeti Stop). See my other post about getting your entry/exit timing right - this is really critical here as it is $$$ wasted if you don't.
Personally I would skip the parks in Rwanda/Uganda unless you want to do chimp/gorilla trekking (both recommended). They are nice but not spectacular and the $150 fee for a foriegn vehicle makes them very expensive. There is lots of stunning scenery in both places to enjoy without paying the park fees and the parks are not known for their prolific game anyway. Cheapest place to see chimps up close is still in Kanyiyo Pabidi just inside Murchison I think. Don't miss rhino tracking at Ziwa (good value, good cause). Visiting the gorillas are very expensive but a genuinely amazing experience.
You have missed off Ruaha in Tanzania which is magial (much nicer then the northern parks IMO). Selous sounds stunning but I've never made in there. You've not mentioned any parks in Zambia - as a minimum get to SLNP which you can do pretty cheaply by comparison with others you've mentioned and is about as good as they get.
The Mara is worth it. You can save here by camping outside at Talek gate but you won't get the best of it as you'll be right in the area all the budget tours congregate (lots of manic matatu drivers). Try and stay in one of the public camps in the Triangle ($25 pppn) at least for a few days.
Good luck and try not to think too much about the costs.
Bookmarks