You don't need any DME to make a starter. You just need wort. Stepping up does require more time, but if are in a hurry why bother with a starter at all? Just pitch a whole bunch of packs of yeast.
One thing I like to do is save wort after brewing. I'll purposely sparge longer- and once the BK is at the correct volume, I'll draw off another gallon or so. I'll boil that down to 1.030 (usually about 10 minutes) on top of my stove, to sanitize and go from about 1.018 (where my sparges tend to be at that time) to 1.030. Then I fill a tupperware pitcher (2 quarts) and freeze. It's not a huge amount at a time, but I usually have some wort (or DME in the cupboard) around for starters that way.
I make 10 gallon batches most of the time. What I like to do is make a starter for the yeast, and then split my 10 gallons into 2 five gallon fermenters. Then, I save and rinse the yeast cakes and divide that into jars for the fridge. I buy yeast only once or twice a year, because then each yeast packages is good for about 10 batches before I buy fresh.
I just purchased $42 of yeast, so I'll be good now until late fall. Starters are a great way to ensure good quality beer by proper pitching rate, plus a good way to save money on yeast.