It depends on the builder - I've found a few now where, rather that being soldered onto the motherboard, the AC plug is actually on a little cable lead.
Like this one:
http://compare.ebay.com/like/3006340...Types&var=sbar
To replace the plug, you still have to tear the laptop completely apart (In the case of the Toshiba L645, it took me about an hour from start to finish, but I work slowly) but for the customer, an hour of labor and a $7 wire is cheaper than an hour of labor and a new motherboard. (!)
However, most laptop repair places will, like Blain, assume it's attached to the motherboard and quote you accordingly. (And rightfully so - it's true in the majority of cases.) You should probably find the tech manual for your particular laptop and verify whether it is, in fact, a cable or not. Then you can negotiate from an informed position.
Laptop Repair: Power plug breaks off
If you grasp the connector and pull straight out it should never break. (Unless someone trips over the wire!)
