Ikea and big lots have been very useful to me. We have a few big lots in my area, I've often had to make trips to several locations to complete a set of Windows, but well worth it for the cost.
I have one set of Windows that is a custom, oversized window. Only option is custom curtains, I got quotes of over $1k! I researched and bought a well reviewed, basic sewing machine for $40. Scrolled through hundreds of pages of fabric auctions on eBay, found a pattern I liked of heavy duty upholstery fabric for $80 for 10 yards, which was more than I needed, but wanted to be safe.
Took me about 12 hours to prep the fabric and hem it properly, using online tutorials as a guide. My stitching isn't great, and maneuvering that much thick fabric through a sewing machine was daunting at times, but they look great now that they are hung, and no one looks at the stitching except me! Good thing I like the pattern, and worth it for the $120 invested. Plus I use the sewing machine to make small alterations now too. 😊