I have an exhaust manifold leak and found out the studs rust and break off.

Does the quote include removal and replacement of the damaged studs? You have to consider that the prices you will find on this site and others for exhaust manifold gasket replacement assume that the job can be performed without any hardware breaking. If the shop has to deal with extracting broken studs, that's extra work, which is, well, extra. Honestly, the removal of studs broken off in a head is one of the least desirable jobs to have to do in a shop. That being said, it is not uncommon to "pad" an estimate for exhaust manifold removal simply because it is the exception, rather than the rule that a job like that will go smoothly. I would recommend asking the shops if they have an estimate on how much they would charge broken stud, that way you will have a high and low range of what the repair should cost.

Do they have to pull the head or lift the cab off as some ford techs do , in order to access the area with the broken studs?