What kind of PB does your friend use? Although I do not live in SIN and never have I cannot imagine it being tough to find there or expensive if its a big brand, ala JIF/Skippy. I know it was cheap and easy to find in mainland China and has been here in HK. While BOM will be a completely different story, I am sure the higher end grocery stores will have it and it should not be $20/bottle. I know there is a grocery store (as of April 2008) near the JW Marriott in Juhu where one could get all kinds of wonderful imported goods. I love poking around such places and found Nutella and other goodies, but forget if I saw PB there. I am sure it was there or it could be ordered.

Clearly there will be all kinds of other such stores across town but this is just what I have seen on the few limited times I have traveled for work to BOM. Good luck!