Depends where you buy from, and what your search criteria is.
SMG makes them cheap.
Being convertible makes them cheap.
Find a hardtop with a 6MT, and the price shoots up. Simple supply and demand, nobody really cares that the SMG/convertible cost considerably more when it was new. The same way a 2001 Jaguar that cost over 80k will now sell for under 5k.
What do I think? Buy yourself an E92 335i for the same price.
PS - The G37's engine is rough at high-rpms, and gearbox/clutch is unecessarily difficult to operate.