There are many inexpensive options available to turn your windows into works of art. It all depends if you are aiming for privacy, beauty, darkness for sleeping, or a combination of the above.
The first step is to think about what you need your treatment to do. In a bedroom, you might aim for very dark, so that you can sleep past dawn. In a living room, you might want something that is beautiful but does not cover the window much. In a bathroom, privacy might be a main concern.Once you determine your basic needs, then it's time to brainstorm about a cheap solution. One that I love is to get sheets or raw fabric and just drape them over curtainrods. If you go on eBay, you can find gorgeous fabrics and even sariis from India with incredible decorations, for hardly any money at all. You don't even have to sew if you don't want to. Just hang the fabric down one side, wrap it around the curtain rod to drape across the top, then let it hang down the other side.
Basic shades are pretty cheap, and come in a number of thicknesses for privacy and darkness reasons. Get some resiliant paint that will be able to handle being rolled up - and a few stencils that you downloaded for free from the web - and decorate! You can use glow in the dark paint for a fun bedroom design, or other decorative paints for more formal looks.
Here's an idea - paint ON the window! Get glass paint and actually paint designs onto the window. This can be gorgeous for a bathroom window, to both provide privacy and lovely decor. You can also get the plastic stick-on variety of decoration to make a less temporary statement.
Don't think of your windows as static objects that will never be touched. Change with the seasons! Put out light, airy curtains in the summertime, so they blow with the breeze. In the winter, switch out to heavier curtains that will help keep out the draft. If you have a gorgeous view, pull the curtains back so you can drink it in. If it's less pleasant outside, let your curtains be the focal point, with their beauty and style.
