The entrance fee to the reserve is R10 per person (and I think R5 per child). The top of the hill is wonderfully cool on hot summer days and the reserve provides sturdy tables and benches for you to sit at while enjoying your picnic - free from ants and other insects who may otherwise conspire to rob you of you rations. :)
If you're unsure of how to find the reserve's parking area - in this post I've added a link to a Google map that illustrates the path to the top of the hill.