CADILLAC CATERA CYLINDER HEAD

1998 Cadillac Catera 6 Cyl Two Wheel Drive Automatic I Just Change My Head And Now I Got A Misfire On Cylinders 1, 3, And5

Is It Alot Of Work To Change A Head Gasket On This Kind Of Car? And Also If I Took It To A Garage How Much Should I Pay To Have The Work...