Find a lady in your area who makes drapes (My wife asked on Facebook and got a dozen recommendations). Have the lady come over and give you measurements. Go to a fabric store and buy whatever fabric you want. Take to the lady...wait a few weeks...hang drapes.
The cost variable will be the fabric. Depending on what you select, it could be a few hundred dollars or a few thousand.
Oh, and the rod can be expensive too. My wife got an acrylic curtain rod that was stupid expensive. The rings aren't especially cheap either.
There are plenty of people who will sew draperies in their home for very little. The cost will be the materials, and what you select.