I take for granted living here in northern Illinois, I was told the sand/gravel mecca of the state, sand is free everywhere.
The sand/aggregate is this case is only being used to fill volume. You can mix cement and water and it will work for this just fine, but uses to much cemnt to fill a good bucket.
Get creative here, I know it's winter but scrape a few buckets out of a gravel drive, lot or shoulder. most stores sell broken bags of everything super cheap, see what you can find.
