Just read something interesting on Box Office Mojo. For all that it’s a box office flop, Cowboys & Aliens is ranked as the seventh highest grossing Western of all time.
Domestically, anyway; everything from Brokeback Mountain to Back To The Future III surpasses it if you add in worldwide gross.
That said, it’s not just that True Grit grossed a hundred million more than C&A has; it’s also that True Grit cost a hundred million less to make, and so raked in six times its budget by promptly crossing the quarter-billion mark. Open Range grossed triple its small budget, Young Guns did quadruple; Unforgiven grossed ten times its budget; Dances With Wolves, almost twenty. So long as it’s just gunslingers riding around on horses, you can avoid a flop by hiring stuntmen and shooting it cheap – but if you build it around sci-fi special effects, box-office results that would’ve been great fall short of breaking even.