I did the math in another forum post:
1400 shared minutes/unlimited text - $100
2 x 2GB data plan - $60
2 x unlimited data - $60
5 x lines - $50
For a total of $270 (minus some discounts) puts me at $217
New plan
12 GB data - $80
5 lines (assume dumb phones are $20 too) - $100
Total of $180 but doesn't include phone subsides
Currently have a G3, Note4, One M9, GS3 and just ordered two GS6.
So that's 4 phones being paid for (approx $100 assuming $25 per phone) puts me at $280 total before discounts. The discounts probably work out to less than I get now (given the phones aren't subject to any discounts) plus less data. Granted, I don't use 12 GB per month between all 4 lines but I need as close to an apples to apples comparison as possible.
So technically it's cheaper if you're not paying for any phones but of course you have less data. Once phone subsidies come into play its definitely more expensive.