help with calculating amendments weights in gallons for my soil medium?

i was recommended a soil mix by another member in the organics section that consist of the following.

1/3 canadian spagnum peat moss (was told to pre wet it)
1/3 EWC
1/3 aeration (im thinking of either going with 3/8 particle lava rock or humus)
mineralization: basalt or glacial rock dust.
DR EARTH LIFE ALL PURPOSE FERTILIZER 5-5-5 (mixed in with my soil) (see below)
he quotes: ("for that much soil you will need about 30-35 cups (so just say 2 gallons) worth of fertilizer (no i don't know how many lbs that will be")
[i will be going for 100 gallons of soil total]

so my grow season is just around the corner starting in late march. i'd really like to calculate how much this will cost total. the problem is i really have no clue how to calculate how many bags of ewc, aeration, canadian spagnum peak, fertilizer etc i need to purchase (will be buying online if cannot source locally). i would feel a huge relief taken off my shoulders if i could determine how much of each i need to buy.

so basically if it's 1/3 canadian peat moss, ewc, and aeration i will need 33 gallons of each. any way i can calculate the products weight to gallons so i don't end up short or buying too much of what i don't need?

There is 7.48 gallons in 1 cubic foot (how most soil is measured). So with that we do a little math and get 13.37~ cubic ft = 100 gallons. Go a step further you get 4.46 cft of each.