Have you tried Awesome Shop USA
http://www.facebook.com/#!/TheAwesomeShop/info
http://www.facebook.com/#!/TheAwesomeShop/info
... I told her valve cover is off and sprockets are visible and in good condition and asked for a price w/o sprocket replacement. She skirted the issue by saying the technician recommends replacing sprockets with the chain because they are all part of the timing system.
I've never worked at a shop that would charge the core and then pocket it, but they do have to charge tax on the core charge, IIRC.
That would be a really crazy thing to do, since I've seen a lot of parts that cost less than the core charge, now that I think of it.
If it was a timing BELT, then there's no need to replace the sprockets because they really don't wear (metal is harder than rubber). But on a CHAIN, it's metal on metal and there's always going to be wear ... you might not see it, but there is. That's why you're hard pressed to find a chain by itself and not as part of a set. Same thing goes for the tensioner and guides.
As far as labor costs, ~$100/hr is typical give or take. As far as part costs go, when I worked for O'Reilly's, most shops would ask for their price and list price. You, the customer, got charged list price. That could be from a few dollars more to $50, $100+ depending on the part. And if said part had a core charge, then a lot of times you the customer pay that too, but the shop returns the core and pockets that money. And from looking on parts.com, it looks like they're quoting you list prices on that chain/tensioner.
As far as labor being different between a belt and a chain, yes, but not really. Slightly different assembly/disassembly of the timing parts, but same process and amount of labor. The front of the engine has to be opened up on both. The timing components both have to come off and new ones on. Personally, I think chains are easier ...