Drink two cups of plain water(at least >750ml) before you go
for breakfast/lunch/dinner/supper.
Down another cup of water just before you wish to bite into the
bread/cookie during morning tea/high-tea/any other time.
I am sure, you will be very filling.
As for the cheap part, Get a big plate of rice and ask for curry
gravy and some vegetable, it will cost you at most S$1 at cai-peng
stall.
This is the way those foreign workers eat at lunch time.
Do not say its mal-nutrition! These workers are even more fit than
you and they work under the sun all day long!
My personal favourite is Instant noodles($0.50) with a bottle of
AAA preserved veg($1)!