I have quite a large collection too and I really am glad I do (well, most of the time)....I rarely have to go buy anything to do a quilt ..I just shop in my stash and usually find pleasing things that go together.........
I always check the fabric section of any store I am in, and I look at thrift stores too...often I find clothes that are really good fabric and just be sure to look well about it, esp to see if it has fade or stain or etc..........I hardly ever spend more than about $2.00 a yard, but often you can find ends of bolts that were a lot more $$ to start with...one of my favorite places is Hobby Lobby...the ends of bolts are often marked down there...also check the remnants bin, never know what may be there.......if you have a local paper that offers free adds, put one in there that says you are interested in fabric... watch for yard sales too........some retirement homes have sales during the year and you can get estate finds that way..........and tell every person you know that you want fabric, if they have any they don't want....