Personally i wouldn't rebuild with used spokes but some do. DB spokes do stretch & over time have a memory so will remain at the stretched length. This means that getting the correct tension again is almost impossible.
However, if the wheel is handbuilt & is only say upto 6 months old & needs a new rim, depending on use/condition then yes i may well reuse them.
You guys need to remember that building the perfect wheel takes practice & time, years for the best. There are many on here that i am sure can build wheels but are they as good as someone who has been doing them for years? Nope.
I had a guy come to us straight out of an ACT wheelbuilding course & i'm not sure what they tought him. He may aswell have built the wheel from spaghetti!
Spokes are expensive but then you have to take into account all the different buttings, lengths, colours etc & the shop can only buy them in 72's or 100's normally. They have to allow for a box of spokes to sit there for months before they are needed again.
As for labour, most shops will charge you £40-£50 for an hours workshop time/service, most wheels take 40mins on average so £20-£25 labour isn't too bad really. A lot of shops will even lose the labour if you buy the rim/hub/spokes from them.
They are there to make a living & stock all the pretty stuff you want to perv over. They have to pay for it some how. People need to support the LBS before its too late & they have gone, i'd love to see your Dell Laptop build an urgent wheel at 4pm the day before a big weekends riding!
J
