You have got to know the people there to get the best price. Most would recommend going to Alan Photo for such stuffs in Sim Lim Sq. Nevertheless, always check out the pricing first if possible to avoid any price disappointment later and also, the "freebies" that comes with the package.
Always check to see what is included in the package and never pay until the package is safely in your hands. Else you may find yourself paying for some accessories which they would say "Ohh this one not included, must pay one!".