Within a hundred meters seems likely. That seems to be the limit for mosquitoes and biting flies and other insects that follow CO2 trails to their blood meals.
Honeybees forage within about 3km of their hive, with great variation in this, but their sense of smell may be more limited. Scout bees probably travel in a direction and stop when they find something that smells nice, as opposed to bee-lining to a distant hive directly (pun intended). If they could smell their food from that range, they wouldn't need the.
While I'd wager nearly all insects have better senses of smell than we do, the distance might not be that great. To get an idea, look at the insect antennae. If they are simple or stumpy, then smell isn't as important for that insect. Antennae that are huge and/or feathered, with a large surface area, will be much more sensitive.
Food is one thing: mates are another. The male cecropia moth can detect a female moth from a mile away! If they can do that, I'm sure some insects can smell a meal from a great distance, but only if they have antennae like these:More questions on Insects: