Ok Jeb this is for you. Last night i did a little calculation with the aid of Home Depot.com. (Boy you guys are spoilt in the US take a look at the Canadian version of that site).
So if one uses 2x6 pressure treated lumber and rigid pink insulation with 3/4 sturdi floor tongue and groove plywood then including poly vapor barrier you are looking at around $1.65 per square foot for a wood sub floor.
So Jeb in your case if i have it correct, you would need to add around $1000 to the budget but you still need to add your epoxy budget to have a wood insulated floor over your concrete slab. I made provision in that price for a few tapcons and some of that tuck tape to seal the poly vapor barrier before you put the ply down.
Sure if we put down hardwood flooring and add the cost of insulation etc it will be higher but in hindsite my fir plywood finish is even a waste. Since i been sharpening planes and had filings off the grinder everywhere, and walked in a little wet shoes the mix of the two turned my floor black in spots. Its a shop, not the fancy dining room.
If i was a good enough scientist (which i aint) i would love to see someone do a calculation of heat loss on a floor with and without insulation spread over time and work out the economics of this over a number of years. I can only believe its a reasonable payback if one considers rising energy costs. Naturally you guys that survive on burning scraps the whole winter dont have that cost but i do.
I figure i plan on woodworking for another at least 20 years. Whats that worth over time.?
Then go back and consider my point of the value of adding a shop to a property and this is a good subfloor for a more decent floor is the building is switched to an alternative use.