My dragons were purchased on May 2nd at a show at 6 weeks old. They are now 3.5 months old. As far as the size is concerned, a local pet store purchased 4 baby dragons at the same show I got mine -the same day. I saw those same dragons (still in the store)about a week ago, and they are all the same size as the day they were bought. They are tiny. My dragons, the same age as those, could almost swallow one whole. This just goes to show that they grow differently according to what kinds of food and how much they are being given.
I've done my best to provide the perfect environment for my two, and they have thrived. Iknow there's the big controversy about UVB lights but I got a reptisun5.0 anyway, and like I said mine are huge for 3 and a half months. Maybe too big. Yours sound fine though. Just give them as many crix as they want.
And to finally answer your question -Definetly start ordering crickets online. Go to either The SuperwormFarm.com or Reptilefood.com and you can get 1,000 crickets for $9.00 plus S&H, which comes to about 12 or 13dollars for a thousand. They have all different sizes. I'd get 1/4" or 1/2" for your size dragon. Buy a plastic rubbermade thing at wal-mart, put some holes in it and you're good to go for probably 2 weeks per thousand with just one dragon.