I don't know that it's cheaper, but I love my Bobbi Brown loose powder. It keeps everything matte without being too heavy. I actually buy the white, because I'm that pale, but it's more like a translucent powder.
I don't know how you feel about drugstore brands, but I've used pretty much everything at every price level and right now I love Airbrushing Pressed Powder from Physician's Formula. I was outside in the humidity all afternoon yesterday and stayed matte.
I use the old school Coty Airspun that I remember my grandmother using (the packaging will always remind me of her). It is like $6. I don't know if it's chalky, but I feel like it's pretty matte.