Al 85mm generally are very good and sharp, the cheapest is the Samyang/Rokinon as suggested by Fred.
Then there is a plenty of alternative in old japanese legacy lenses, i like a lot the Zuiko 2/85 but it is very soft wide open.
With good sharpness only at f2.8 wide open rhe contax G is a good alternative, but they need clumsy adapter and sometimes need new lube, the CY Sonnar 85mm got same optic scheme.
There il even the Viltrox that have autofocus.
From many users, I learned that Samyang AF 85mm F1.4 is very sharp, but main issue is its variation. Some very fine , but the other is not like the other one. If you buy bad copy, it is worse than Sony 85mm f1.8, but good copy is closer to Sigma 85mm f1.4 DG DN (sharpest ever for Sony system). That make me hesitate to but it.
