The cost of issuance in the residential mortgage-backed securities market is coming down, with the latest issuer Firstmac shaving 15 basis points off the price it paid for funds a few months ago.Firstmac has raised A$600 million of funding through an issue of RMBS, Firstmac Mortgage Funding Trust Series 3-2016, paying a margin of 135 basis points on the senior notes.The $510 million of A1 notes, which have a weighted average life of three years, were priced at 135 bps over the one-month bank bill swap rate.The $42 million of A2 notes, which have a weighted average life of 3.8 years, were priced at 190 bps over the swap rate.The B notes, worth $35.4 million, were priced at a margin of 245 bps, the C notes (worth $6.6 million) were priced at a margin of 325 bps and the D notes (worth 4.6 million) were priced at a margin of 580 bps.Firstmac retained the D notes, which are worth $1.4 million.When Firstmac last issued in the RMBS market, in May, it paid a margin of 150 bps on the senior notes, which had a weighted average life of three years, and a margin of 210 bps on the A2 notes.The pricing on Firstmac's latest deal compares favourably to recent bank deals. Bendigo and Adelaide Bank paid a margin of 133 bps on the senior notes of a $700 million RMBS issue in August.