Apart from Ananas, The Cafe Lobby is another "economy" choice
follow by Japanese Umi Sushi (some said cheaper than other japanese
stall in the food court) and if you are just interested in snacks
like salt buns, butterfly bun and you tiao etc, there are this
snack franchise that operate in MRT or bus interchange like "Tiong
Bahru Tian Bo Shui Kueh" etc. Finally NTWU canteen is the cheapest
eateries that operate in almost all bus interchange
although priority is given to bus captain first.
For the issue of Republic Food Court, I think it business is
just another "tourist trap" mean for overseas traveller. For a
caucasian, their western food like fish n chip, rib eye streak etc
would cost about a range of $20-30, so they will not see a
different in eating at Republic Food Court, still maybe local
"towkay" belong to another group who didn't mind going to
restaurant or Republic !