Well since you're into math...let's play.
30 pallets x 2450/pallet = 73,500lbs or 36 ton
36 ton x $75/ton = $2700
73,500 / 50 (lb bags) = 1470 bags
1470 x $3.70/bag (I buy truckloads, not from home depot) = $5439
Wow, you're right, I'm $2739 in the hole. Wait, now let's calculate productivity.
I can only load 800lbs in my spreader, unless I buy a Vbox (which would be paid for in the first year w/ savings, I understand that.) So I have to pay a driver to come back to the shop twice per night, so we lose 2 hrs total, per event
2 hrs x $150/hr = $300
$300 x 20 events (avg) = $6000
It now costs me $6k to use bulk, but I did save $2739
$6000 - $2739 = $3261
I haven't even bought a skid to load it or built a place to store it. I have 5 properties that account for almost all my salt. All 5 properties are tied into the hospital. What happens when they decide to pull it in house, give the lowballer a try, or just start busting balls and eliminate the salt (which won't happen.) For me, bagged salt works. I make ALOT of money when the snow flies. I buy new trucks, put the biggest plows on them money can buy, and pay my guys well. I could probably make due with older trucks, smaller plows, and unemployed crackheads. The $2700 it might "cost" me to use bagged salt is a drop in the bucket for the benefits I might see. I understand for most guys it's a no brainer. If I had a skid steer that was just sitting in the winter and a huge empty pole barn or mafia blocked pad to store the salt, and a Vbox in a dedicated salt truck...sure I'd use bulk. At the end of the day there are many more variables to a business decision than dollars and cents.
Or another option would be to buy a load of bulk salt and pay my guys to put it into bags for me. Just kidding. What kind of leunatic would do that.
So...about that spreader