Answers

I suggest take a look at the ProVia Endure high grade vinyl window. 

Triple pane is what I sell now and has very low U-factor and air infiltration.

I love their low profile slim casement window, just amazing.

The quality is nothing I seen before in my 22 years in this field.

Available in new contruction nail fin.

https://www.provia.com/productdetail/vinyl-windows/endure

Installation is very important, good window + poor installation = Problem.

Cost varies from contractor to  contractor. Check with your local building supply stores that carry ProVia products (not HD and Lowes) or go to PorVia to find a dealer. 

Suggest you request bids from several dealers and supply stores with the same specs

Best wishes

Edgar makes great points of matter in regards to the window selection and the Point of Insualtion. We SPray Foam Every New Home and are extra focused on sealing the envelop properly. We are located in a sub tropical climate and the principles apply adversly although nearly the same.

We ar eable to achive Power bills from 60-160 dollars on homes from 2000 sqft to 6500 Sqft. Air Loss, Insulation, and proper install of product

PROTIP: Watch ou twith the Term "Builder Grade" A Seasoned Window and door expert from Lowes will educate You on who makes the  "Builder Grade" windows You might speak of. There is a lot of " Razzle Dazzle in Windows and doors"

Check the performace & Rating. Do Not get Oversold and get a solid warranty orinated window.

Remember if they are not installed correctly and sealed IT does Not matter.... air flow is air flow... Loss =Loss

Billy Gavigan

Great Question!!