Yes: more specifically, the staff canteens at the airport are open to the public, serving authentic and tasty Singaporean fare at rock-bottom prices! Despite the name "canteen", these are mini-hawker centres with a dozen or so independently run stalls each specializing in specific dishes/cuisines. There are at least three of these:
The one you'll never find by accident is next to Terminal 2: head out from Customs, turn left, cross the road, enter the carpark (2A) and take the elevator up to level 3M, which is marked "Staff Canteen". Here's the illustrated journey, photos mine:
There is a similar but newer one in Terminal 1, detailed instructions here. TL;DR: find Row 13 in Departures hall, take lift at end down to B1.
The least secret of the three is the Kopitiam food court in the air-conditioned shopping mall below Terminal 3 (level B2), between the MRT station and arrivals: just follow the signs for "24 hr food court" right after Customs to take the escalators or lifts two floors down. This is slightly more expensive (meals from around S$5), but it's also air-conditioned, attractively presented and has a good selection of halal options:
...and still half price compared to the airside food courts.