Can anyone tell me what the rough price difference between Decora-style switches and receptacles and standard-style switches and receptacles is?
Decora:
http://www.leviton.com/sections/prodinfo/decora/deframe2.htm
Standard:
http://www.leviton.com/sections/prodinfo/receptic/reframe2.htm
Just curious b/c we’re building a house and, while we like the Decora rocker and slider switches, we could give a rat’s ass about having Decora receptacles rather than standard (rounded) receptacles.
Of course, if the price difference is insignificant, then we’ll go with all Decora. If it’s a huge difference, we’ll just have mildly mismatched switches and receptacles. 
I am not sure what the Decora switches cost but standard switches and receptacles are pretty cheap for contractors. Maybe like less than $1, from my experience at Home Depot. A designer switch like Decora (all I know is what I saw in your link) is still not a huge expense, let’s say $5-6 per basic switch, maybe three times that for something like a motion sensor. But it adds up. In a house with 4 BR, 2.5 BA, LR, DR, FR, kit, den, you’re probably talking around $150-300 extra for 25-30 switches and maybe $500 extra for 75 receptacles. Probably not a big % of the house cost but every little bit adds up.
However, since you’re building the house, you should just ask the builder for the price difference. I don’t know if labor for installation is the same. And they may take a fatter markup for upgraded components.
At lowes.com:
10 pack decora-type switches: Single Pole 18.96
10 pack regular toggle switch: Single Pole 4.41
Get the Decoras. They cost more, but you can use the same plates for both switches and outlets. When it comes to selling a house, the Decora switches are a great cheap update that gives an otherwise nondescript room an upscale appearance. Also, with plain Decora switches, they’re easier to turn on and off; just a quick swat as opposed to a careful list or push with a standard toggle.