There was another member not too long ago that had his repaired - he posted before and after pictures. He wasn't very pleased with the job as the shop didn't smooth off the welds etc - basically poor craftmanship. Mine is cracked right by one of the bolts that holds the latch to the jamb pan on the door. I used a small fender washer and tightened the bolt as much as I dare until I can mig it from the inside and outside.
My guess for the best reapir is: remove inner door panel, window all the way up, remove latch device, make sure there are no other parts/wires etc in the way. Tape off and area you are comfortable removing the paint from on the jamb. Grind, sand or whatever you choose to remove the paint along the crack, drill a hole at the end of the crack where fresh metal is so the crack will not continue to creep along after the repair. Make the cracked sides level with each other and mig a spot to hold then stich ending at the hole - fill the hole with weld. Do the same on the inner of the door cavity. Grind high spots down, putty, smooth, prime and paint. I doubt you should need a new door.