I rarely, if ever, buy glass cleaner. Actually, I can't remember the last time I bought it. Instead I make my own. It's much more economical, and it's easy to make a batch whenever you want. Every time I make glass cleaner, I am baffled at how expensive it is in the store compared to how inexpensive it is to make at home.
You can either use an old glass cleaner bottle that's been rinsed out or pick up a couple of spray bottles at the dollar store. I have two different recipes I use. One is for harder to clean stuff (like doggie nose slobbers), and the other is for mild cleaning just to freshen up the windows.
Here are two recipes:
2-3 tablespoons nonsudsing ammonia*
1/2 cup (4 oz). rubbing alcohol
1 drop dish soap, no more, no less (can omit but solution doesn't clean as well)
Put ammonia and alcohol in a spray bottle. Fill almost full with water. Leave about 1/2 inch of space below the top, then add the 1 drop of dish soap. Put sprayer on the bottle and tighten. DO NOT SHAKE. Instead, tilt back and forth about 20-30 times to mix. It might be temping to dump all this in the bottle, but if you begin to add water, the dish soap will foam up, and your ingredients will start spilling out of the bottle. You will recognize the smell of this, as it will smell just like Windex. You can even add a drop or two of blue food coloring, just for fun.
Window Cleaner Recipe #2
Approximately 1/2 cup white vinegar*
That's it! Put the vinegar in a spray bottle and add enough water to fill the bottle. Cap with the sprayer mechanism, then shake to combine. This works great but can smell like vinegar while you're using it. The vinegar smell leaves once everything dries.
I currently use the vinegar solution with microfiber cloths. These work great because they only require a small spritz of cleaner to clean a whole window, and they're very absorbent, so you only need one cloth to clean many windows. Combine the two, and you only need a small squirt of cleaner, and the windows come out clean, shiny, and streak free.
*Keep in mind that if you have hard water (i.e., water that contains a lot of minerals or metal particles) you may need more ammonia or vinegar. These recipes are flexible enough that you can adjust them for your cleaning needs.