Let's look at fabric first, because that's the main thing you'll need to make any type of inexpensive curtain. Pick the cheap ready-made curtains fabric you like best. The best curtain fabrics are cotton, linen, polyester, and microfiber. These fabrics just seem to stay looking good longer. Avoid quilted fabrics which can lose their shape and silks that won't hold up very well. To measure the amount of fabric you'll need, you can use this rule of thumb: The fabric needs to be twice as high as your window and three times as wide.
They can also allow users to control the amount of light that enters their room. You may also lift the blinds so that more light will enter your room. Curtains do not offer such control.
For some, decorating a bay window is an impossible task. But it doesn't have to be if you take it from each section rather than trying to decorate it as one large window. Each window section will have its own bay window curtains on their own curtain rods. They should be of the same tende personalizzate fabric and design but they should be treated as separate window treatments. Many times they come in sets so unless you are making custom curtains you won't have to worry about sizing each window.
The style panoramic glass curtains of your custom window treatments also needs to be considered. Your home style will determine this to some degree, but there will likely be some leeway in what you choose. There are so many options today, that it might be difficult to make a final decision.
If you would like to take advantage of the insulating advantages that some curtains offer, then to make draw curtains a more formal presentation, you could combine a valance over the top edge of your curtains to complete the look.
There are more expensive means for keeping a house insulated, such as making sure there is airtight insulation throughout the entire home. Be sure that no matter whether your solution is cost effective or more expensive that you stay warm for the winter and keep your heating costs down.