Easier to just buy 5 packets of yeast then for 15 gallons of 1.065 wort and sprinkle appropriately. That's $25. Or rehydrate and count on 4 packets. That's $20.
It's still more than building a starter, but yep, if you factor in the time/effort to use a starter can for 1L ($5) + 1/2 lb of DME for the 2L ($3?) the time costs, Then you're only saving $10-15 bucks for 1 hour of work. That may be worth it though.
ASSUMING US-05 is 18 Billion cells per gram conservatively (debatable, but I would agree with this and I think most would), then one packet is not quite enough but close (and arguable) for a 1L + 2L step starter to cover such example, but 2L + 2L is should cover it with ease, though. In a 2L + 2L example, then DME is the only thing that makes sense. That's $6 + 2 hours of "work".
Just trying to think for the future. Thinking out loud.
I typically use 1.5 packets for greater than 1.060 (obviously, up to a point) without rehydrating as my go-to rate for Safale.
Brewing for myself making starters from dry yeast makes zero sense. I'm trying to think ahead for group brew days where US-05, S-04, or Nottingham is called for and my equipment is being used to make a double, or triple batch!