You can go to a thrift shop to pick up bed sheets as a cheap source for fabric. This could be used instead of muslin for your trial runs, as lining, or if you find a cute vintage print as your main fabric. This chart is useful though to figure out how much yardage is actually there.
Pom pom curtains and curtain tricks you might not know. Fake pleats... I like curtain rings because they are easy to slide back and forth. My mom taught me this little trick, to gather the fabric in a little pleat before clipping on the ring. It’s an easy detail to make your curtains look more custom.