That is a whole other can of worms, discussed all over the place here! Generally there are 3 types of overhauls: Student, Pro, and Artist.
Student overhauls generally just consist of a repad and recork. Very basic. Doesn't address unlevel tone holes, any modifications or customizing, just a general setup (no custom setup for the player). It's what some techs call a "re-pad" or "bringing it up to playable condition" (note that some techs will do less to bring into playable condition. This may mean having to come back again though, to get something else fixed, so many techs won't do this, on account of their reputation). Generally between $250 and $400
Pro Overhauls is what most people here do and get. It's a complete repad, recork, the works done the sax! Everything except replating/lacquering. Some include customization, and all include a customized setup for the player. These take longer, and cost more, but are much more thourough. Tone holes are leveled (when needed), everything is replaced or repaired (as needed), and it plays like a new sax (well, as new as an old sax can be
). You often get the choice of pad brand preference as well (which is usually at an additional cost).
Artist Overhauls is all that plus all the "bells and whistles". The sax is can be customized to any extreme (this includes putting modern keywork to a vintage sax. There are few techs that can do this, they do exsist! It usually includes refinishing, can include custom engraving, and usually exceeds the re-sale of most saxes it's performed on. This is for the player that will die with their sax!
But, these are just generalizations, and one must ask local musicians who they trust with their saxes, and ask around here too. Every shop is different, and some will do more than others, and some have much higher standards than others. There are also many shops out there that will try and rip you off (think the stereo typical used car salesman). Just have to weed through the crap to find the diamond!