I may see you there!
It depends how serious you are about getting good photos.
The general advice for 24hr races like n'ring and LeMans is to not bother! Just enjoy it.
However if you're ok with some faffing, buy some used gear and sell it again straight afterwards. You should only loose postage.
But seriously consider renting.
As a minimum you want a half capable (prosumer) body and a 70-200 2.8. Although having never shot the circuit i can say how much use 200mm will be. I suspect it will be well short - but you may well want the 2.8 later in the evening, so its really the only practical option.
You may also want a wide lens, 10-22 Canon or 10-20 Sigma would be perfect for the light trail shots (also going to need a tripod).