just get a sigma 70-200 f2.8 2nd hand from BnS if money is the concern, it's ranging from S$600-1000 depend on the version and ur negotiation , and it's a damn good lens...
sample of the pic taken with sigma 70-200 HSM(version 2 of the sigma 70-200) at F3.5:
sample of the pic taken with sigma 70-200 HSM(version 2 of the sigma 70-200) at F3.5: