Black Soldier Fly larva seems like a hands down winner here.
You can get them for about $25 for 1,000 of them, and for a single lizard at that age I'd assume you probably will need to take about 50 of them out at a time and "feed" them on stuff like bread and tomatoes or baby food, etc. in a separate container, and keep the rest in their shipping material at about 65F.
You'll read some stuff that says to put the ones you re feeding on a heating pad, but honestly its not needed especially if your dragon is small anyway.
You're guy will probably eat between 4 and 8 of these a day depending on their size.