A new exhaust manifold can cost between $100.00 to $800.00 just for the manifold depending on make and model of vehicle.
Then if you have a shop replace the manifold then it'll cost another $100.00 to $300.00 in labor charges so it's hard to tell exactly how much the exhaust manifold will cost to replace unless we know the make and model of your vehicle.
But if you have a shop replace the manifold expect to pay $200.00 to $300.00 on the low end and around $500.00 to $1,000.00 on the high end depending on make and model of vehicle.