What are your typical material costs for building a subfloor over concrete for a SOG 3/4" hardwood installation? Do you build a floating floor or do you anchor one sheet of 3/4 cdx to the concrete?
Or are you doing glue down? What are your material costs in this situation? Do you find your labor increasing as a result of choosing one installation over the other? What method is the best? I've received contradictory advice on these subjects.

I'm thinking about adding Hardwood installation to my portfolio and wanted to know what I was getting myself into with regards to cost and labor. Any advice would be greatly appreciated

Let me start by saying that my family has been in the wood floor buisness for 80 years. We do not have time to risk our reputation by cutting corners now. That said we have multiple steps for installing a floor over a slab.
1) we lay out 6 mil plastic in the room.
2) fold half the plasic back on itself and roll on non fibered roofing tar with a 3/4 roller
3) carefully fold the plastic back over the tar and lay out 5/8 CDX laying perpendicular to the final floor spaced 1/4 apart
4) nail down with 1 1/4" nails with powder actuated nailer about 25 per sheet
5) roll out 15# felt
6) nail with 1 1/2" nails in powernailer

Our cost for the subfloor portion is about 1.25-1.50 sq/ft we charge 2.50. By far and away this will give the best floor that will outlast any floor out there. Most contractors miss the tar (it is a huge hassel and mess) but every nail holding the plywood down cuts a hole in the plastic and the tar seals that hole, otherwise the plastic is pointless.