running marathon and look for shoe? I figure you have not been
running much.
There are specialist shoe shop in Penisula and Funan and Marina,
but i find Novena is a better option.
try out the shoes shop in Novena Square, most of the shoes
shop representative there are equip with answer to your shoe
query.
Do remember to tell the sale person you are doing 42km, as most
probably you will be recommend to get 1 or 1/2 size bigger.
Bring along a old pair of sneakers along to the shoe shop. Be
prepare to do some running on the treadmill while trying out the
shoe...so get the proper attire and no heavy food before going up
to Novena.
The most popular around is Asics, New Balance and Nike for
long distance running.
I assume you are not doing off trail/cold weather(snow)
marathon...which require shoe of different type.
Price wise in Singapore is pretty standard...as for discount,
you might be getting from 20-50% off the retail depend on what
brand and which shops and lobang you can find.