The problem with the wooden ones used to be that they were made in China of very cheap material and no two windows seemed to be the same. We've been producing styrene windows for doll houses for many years and they are popular with doll house manufacturers because, being injection moulded, the dimensions are consistent - important when you're cutting out hundreds of doll house kits on a cnc router.
Although our garden railway sized windows are 1/24th scale, a window is a window and they usually look right. Strictly speaking the doors are a bit on the small (short) size, but there are ways to get around it.
The easiest way to get the prices is to download the price list from our web site
http://www.jacksonsminiatures.com/RETAIL.pdf The door and window prices are on page 8. The prices shown include 20% sales tax (VAT), so divide the price by 1.2 to get your cost (or multiply by 5 and divide by 6). As a G Scale Central member I'm sure we can do something about postage, though because the items are light, it wouldn't be much anyway.
I hope that helps.
Cheers!
Steve