I am planning to event a fence this summer and, given the size of ~ 250 linear feet, am looking for the cheapest option for cementing the poles. I am considering the use of metal Postmaster (MasterHalco) posts and plan to set them 4' in the ground in ~ 8' holes as I am up north and the frost line is ~3.5 feet.
I have checked out multiple types of fast dry concrete specifically designed for fence post but would like to find a cheaper option. Is a standard portland concrete mix acceptable for this application? If Yes, what ratios of cement/sand/gravel should be used?
Also, are sonotubes recommended?