I see a bunch of questions here as you look like a new cham owner.
I'm also going to base my ansers on the fact that you are getting a baby.
(something around 10-16 weeks old...and realy small, say 2" nose to vent...tail not included)
you should be feeding something around 8-12 crickets per day.
half in the morning, the other half in the evening.
you will need to feed other insects too like phoenix worms...maybe half what you feed in crickets (4-6 per day, on the days you don't feed crickets).
crickets can be "cup" fed, and I do have a cup regardless that I almost never use it.
I personaly feed "dusted" crickets by hand in a small cup, or I hand feed them by holding one at a time with my fingers.
my baby already knows this hand feeding cup and goes crazy fast to the frount of the cage ready to eat the second he sees it.
lately, I have been taking this cup and putting it up against the screen of the cage to release one cricket at a time, so they start to crawl upwards on the screen....my baby goes nuts with this type of "free range" feeding.
you could also just "dump" them on the bottom and they will climb up the screen for your baby to eat as well....but they can also get wet on the bottom of the cage between mistings, and drown, so I don't do this anymore.
I only "cup feed" (not hand feed with a cup) when I don't have time, and just dump them in.
phoenix worms don't need to be dusted and should be put in his feeding cup.
now, there are some great places to buy crickets online.
you'll need 1/4" crickets, and lots of them.
some of them will grow, so feed off the larger ones first if posable.
yes you can buy some crickets from your local petco/petsmart or petland discount. yet they are normaly 10 cents per, plus tax.
you have to wiegh just what is cheaper in the end.
I would advise that you don't buy in bulk. say 1000 crickets, as they will grow faster then you can feed them off and then you'll be stuck with crickets that are too large to feed.
above all, please read alot of posts on feeding and dusting.
if you have any more questions please just ask us....or you can PM me.
good luck,
Harry
edit: I see you already got some good advice as I type way too slow, but if you have more questions, please ask.