I try to buy quilting materials on sale too but I like batiks and Early American and 1920s/1930s reproductions and while Joanns carries good fabrics not a lot those so I end up in the quilt shops.
However I try to buy end of season or end of bolt fabrics and can save 20 to 30 percent that way.
Also if someone is giving a class and it's in a fabric store sometimes they give a discount on fabrics if you buy something during the class.
I have spent as little as under $50 and as much as $150-$200 depending on size of quilt and sale vs. full price.
I also have joined a quilt guild and they have a "fat quarter raffle" on a monthly basis - if you donate fat quarters they give you one raffle ticket per fat quarter you donated and then they divide up the fat quarters into four or five piles depending on how many were donated and throw the tickets into a bowl and pick one for each pile. We have a large guild and sometimes people donate more than one fat quarter so there might be 10 to 15 fat quarters in each pile. I have won several times in the past five years and ended up with either enough to make something or enough to fill out some other projects. Also made some nice scarves and some small baby quilts and splurged for the backing and batting and donated them to the guild for the next Christmas when they take quilted donations to the local shelters/food pantries.