Miniatures and small scale sewing requires fine fabrics and even a small amount of fabric can get expensive. You can recycle various common items into wonderful doll costumes. A linen handkerchief or napkin come with rolled hems usually done by hand or machine. If you can find one that would no longer be useful for daily use those finely crafted hems can become the hem of your doll’s new dress or sleeves!
Silk blouses are also a common item that get worn spots rendering them unwearable but the rest of your former blouse can be used for your next project!
Personally I like to purposefully get blouses and such at thrift stores and second hand shops. I tend to buy items that are too small for me and usually on a sale rack. Once in a while I find a blouse for myself, wear it for a while and when it wears out use it for a doll outfit.
I keep my nice fabric in totes by color so I can find what I need or want.