Safari in Maasai Mara on a real budget, is it possible?

Yes, but you need a group camping safari, which runs 1,200–1,800 USD for 4–5 days including park fees, transport from Nairobi, camping gear and a cook. Stay an extra night in Nairobi at a backpacker hostel to catch the shuttle. Avoid the cheapest unmarked operators, they often cut park fees.