That sounds like alot of extract to use in a starter, but I'm no math whiz so I am not figuring out how big your starter is.
You can pitch the whole starter into your wort, then you don't need to go buy more DME.
I keep a 3 pound bag of DME in the cupboard, just to use for making starters. I use 1/2 cup to 2 cups water, usually.
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