You can get Vietnamese pork rolls fairly cheaply, but cant remember exact price. The Korean spot at the end of the sussex centre food court has a huge menu. From memory meals are from $7.50 and they include a little soup, rice and the dish.
Another sneaky and cheap food court to try is the one under Woolworths, entrance from Pitt St (around the corner from Lowes, just look for a photo shop and you're there).
Not sure if there is anything around the $5 mark but definately plenty under $10. Look for the Hianese chicken ... you'll find it by spotting the longest line. Delicious! And I think only $8.50. Also comes with bonus soup. over 8 years ago