It can be a more than just window A and window B. No two windows are a like. The build quality, glass quality, and add-ons (argon gas, capillary tubes, etc) can all affect the price. Some companies use different types of film for their Low-E and HP Low-E film they use.
And sometimes you pay the price for the more known name brand because they will give you less hassle if you have to do any type of warranty or replacements that need to be shipped.
You get what you pay for, remember that.
|