@Larold This right here. I think we are all assuming that the 7 digit (or whatever) mark that you are placing on the chips is for security? Is that correct? If so, and security is an important issue, then the last thing you want to do is buy the cheapest possible chip, that anyone can easily buy, then mark your security code on that chip with a sharpie. You might as well have no security at all.
Tina no molds are the easiest cheap way to do this.
The absolute cheapest way is to purchase cheap slugged chips that will take a one inch label, then self produce a unique label that you can laser print onto Avery labels, which can be bought in bulk for around 3-5 cents each. I did this myself 3.5 years ago when I was a super cheap tight ass. Quite a bit of work, but cheap if you do it all yourself. If you're truly interested, say so and I will point you to a couple of posts where I documented how I did this. You might be able to keep your total cost at under 20 cents a chip, and you'll have reasonable security that someone won't copy your design and print their own labels.