My own situation, tho, sort of condemns me to buying sacks--of something or
other.
The pouring location is remote from a drop-off point, miserable to transport
inside, AND I'm only able pour an approx. 3 foot by 14 foot patch at a given
time, approx. 6" deep, for about 21 cu ft--more than I would want to mix w/

It's still worth asking a concrete co. if they think they can get
a truck in there. Worst that can happen is they say "no".