Westpac has shaved several basis points off the cost of its mortgage securitisation funding, with the pricing of its latest issue of residential mortgage-backed securities coming in below 80 bps.Westpac issued A$2.5 billion of securities - up from $750 million offered at the launch of WST 2014-1 Trust early last week.The bank will pay 78 bps over the one-month bank bill swap rate on the $2.3 billion A tranche, which has a weighted average life of 2.8 years. Pricing on the B and C notes was not disclosed.Last September, Westpac paid 85 bps over the swap rate on the $2.1 billion A tranche of WST 2013-2 Trust, which had a weighted average life of three years.In February, Commonwealth Bank paid 80 bps over swap on the top tranche of its $2.5 billion Medallion Trust RMBS issue.