The part is hardly expensive!
http://www.maplin.co.uk/3.5mm-stereo-chassis-socket-1189
As long as the technician knows how to quickly get inside your netbook, the labour cost shouldn't be very high either.
The only problem might be if the old socket is glued (or similarly bonded) to the case, rather than a screw fit. It might be a fiddly job to get it out without damaging the casing of the netbook. Even so, the technician might simply be able to bend the piece of metal in the old socket (that's meant to break the circuit to the speakers when you insert a headphone jack) back into place.
Phone around for some quotes. Places like PC World charge £30 (+ parts) for a job that only takes a minute or two; independent repairers might be far cheaper.