So I can get 14-2 NM w ground at the big store off the spool for something like $0.43/lin ft w/out tax. I can buy 250 ft of 14-2 NM-B w ground prepakaged on the shelf behind me for something like just under $60, tax not included... compared to $107.5 at the spool price. Don't know the grade of the spool I'm afraid... this is for in house, not damp areas... electrical outlets and light fixtures.

Any difference in the quality here? Copper? Sheathing? Or is it just the in store price for buying convenient quantities? I know, for example, that I can get copper plumbing much cheaper though a friend who works for a wholesaler... the markup there is just crazy. Any reason not to buy the cheaper wire? In the pkg the cheaper wire isn't as broad across MAYBE, so I'm wondering if its less insulated..?

I've heard there are diff grades of 14-2 but I cannot find out any info on this. My DIY books have nothing and online hasn't been too helpful.

Nonmetallic cable, aka Romex, is classified by three catagories;

NM= 60 Deg C wire indoor use , not allowed in new homes for lighting fixtures.
NM-B =90 Deg C wire indoor use only
NM-C = 90 Deg C wire cable can be used in corrosive locations.such as barns.

This is a brief listing of the cable types, enough to show that there are differences in the cables, and the reasons for the cost differences. Need to check the class of cable before purchasing and using the incorrect cable for the application. Let alone spending more money than necessary.

I would be careful of the low cost cable, may be only NM, which cannot be used to connect to lighting fixtures.

I agree with TK that different types of NM cable would have different prices. Sometimes the big box stores have different cable available on the spools for different applications, so when comparing prices make sure you're comparing the same cable type. As long as the cable is UL approved and suitable for the specified application, as TK detailed, you should be OK. The reason for the price difference, assuming like cables, is that it is just cheaper to carry the cable in bulk rather then sell it by the foot-all stores do this. At Home Depot, 500 ft. #12 solid copper-$61 which is approximately 12 cents/foot, off the spool, 28 cents/foot. I work on cars a lot and it's the same-automotive hose by the foot is always more expensive than the prepackaged stuff.

On return trip they are both nm-b rated. Doesn't look any different in insulation thickness.

I'm thinking its just a profitmaker markup like the copper.

Thanks all for the input.