No, the contractor is not going to skimp on the cost of his sand. Sand
is probably the least expensive of the materials he's going to be using,
so it's not the place to look to save money.
What you'll find is that people that do a particular kind of work get to
notice subtle differences in the materials and tools they use, and they
soon adopt favourites because they prefer the subtle differences of one
brand of pointing trowel over another or one company's sand over
another. But, also, and as often as not, they buy the same materials
from the same suppliers year after year because they've never felt that
they could have done a better job or did it faster or easier had they
used someone else's materials instead.
So, the contractor is going to use whatever materials he likes the most,
or whatever he's always used regardless of whether he's doing your house
or someone else's. It's simply because he's got reasons for liking some
of the materials he uses, and doesn't have any reason NOT to keep using
other products he uses.