cheapest i've tried so far for 4R is 20cts from Konica Lab at East Point, Simei (applicable to dev+print only. reprint will cost 30/35cts). IMHO, so far the print I get from there is very professionally done, can't tell the diff betw photo print there vs those printed in Colour Lab.
For those who might be interested, here's shop:
Home Photo Center
Eastpoint Mall #01-04
Tel: 6786 6948