How old was Kurt supposed to be anyway? I mean, I find it a little broad to believe that someone who is seemingly a teenager (or, at least, very early 20s) is the owner and founder of a humongous burger joint that was also supposedly going to expand into a chain of its own. Yeah, I know it's a kids movie, and not entirely impossible (apparently, there's a 14-year-old girl in Florida who is quite a real estate tycoon), but still...
He could have been intended to be in his late 20's or early 30's; even 15 years after the film you can find college-age "young adults" and graduate students that have the same style and personality as Kurt (mostly in Business-based fields). Further, he has a distinctive edge over his competitors: it seems like he's giving more burger for the same cost. And all this is before considering the connections he has in order to have initially acquired his illegal chemical additive; he could have been well-off before he started his business.
What exactly was Ed's sauce again in Real Life? I seem to recall reading or hearing that all it really was was a mixture of ketchup, mustard, and mayo in the right ratio to give it that bright orange color, but I don't remember that coming from a confirmed source. It would make sense though. Oh, and let's be honest: the sauce was pretty much orange because this was a Nickelodeon movie, wasn't it?
How did Dexter not already know that Mondo Burger used illegal chemicals to enlarge their burgers? Yes, he only worked there for a short time, but you could clearly see the triampathol boxes and cans on the shelves.
He didn't work in the kitchen, and I guess only Kurt's most intimate employees know it.
Actually, he did work in the kitchen: "BUN! PATTY! TOPPING! SAUCE! ASSEMBLE! BUN! PATTY! TOPPING! SAUCE! ASSEMBLE!" I think Dexter was so caught up in the misery of his summer plans being busted by having to work a summer job to pay off his mom's and teacher's cars that he just didn't really pay that much attention to anything else that went on in the kitchen aside from Kurt's Mondo Goons yelling orders at him.
How was Mondo Burger able to charge the same prices as Good Burger? Using a black market chemical to enlarge their burgers would probably end up costing them more than simply using more beef.
Because they weren't selling the chemical, they were selling the burger, that's why they charged the same price as Good Burger - all the chemical did was enlarge the patty without them having to use more meat, therefore, not using more meat doesn't require them to charge more. As for using obtaining the chemical, they could have had connections that got the stuff for them at a reasonable price so they didn't suffer any significant losses; remember, Kurt seemed to have high friends in low places.