Jkelton is right on.
I also own a blower company.
We will not do anything under 10 yards, like Jkelton said, It is just not profitable for us to do so. Also on jobs that do not have large beds and are mainly tree rings we tend to charge per tree ring. This is because tree rings for a blower truck take small amounts of mulch but more time. they are tipicaly place a decient distance apart so it is eather alot of hose draging or movment of the truck. Every time we have to shut down the truck to move or add or subtract hose it eats up time. Time in our business is key, more time less mulch = less money. So i would say anything over 10 yards of mulch and not compleatly covered in tree rings or small beds that are cut up around the property should be done by a blower truck. It will save you time and money. 280 yards would be a good amount of mulch for one location we have done larger amounts than that but not typicaly at a residential location, but i must say we have done a few larger amounts than that at residentails but they are typicaly large estates. just my 2 cents