The cost of wholesale funding in one sector of the domestic debt market is rising steadily, a trend emphasised by the price attained by ING Bank (Australia) on its second sale of residential mortgage-backed securities for 2011.The spread paid by ING Bank on $750 million of RMBS priced on Friday was 25 basis points higher than the spread available to the bank in the market for mortgage securities in the middle of the year.The spread is also 35 basis points more than the pricing available to major banks early in 2011.ING will pay 135 basis points over the one month bank bill swap rate for its top tranche that comprises $598 million (or 80 per cent) of the issue. ING sold the bonds through the IDOL Trust Series 2011-2.The $100 million A2 tranche, a five-year soft bullet note, was priced at a fixed rate of 5.5 per cent. The bank did not disclose pricing on the other tranches, worth $52.5 million.ING Direct's pricing continues the steady increase in the cost of RMBS issuance by banks. Last month Bendigo and Adelaide Bank paid 130 basis points over the one-month bank bill swap rate for the top tranche of its Torrens Series 2011-2 Trust.Two other RMBS deals were done in October. Bankwest (a subsidiary of Commonwealth Bank) paid 125 basis points over the one-month swap rate for the $365 million A1 tranche of its Series 2011-1 Swan Trust. The tranche had a weighted average life of 2.2 years. ME Bank paid 125 basis points over swap for the $622 million A tranche of SMHL Securitisation Fund 2011-2, which had a weighted average life of three years.In early October National Australia Bank and Westpac sold the primary tranche of RMBS securitisations at 120 bps and 125 bps respectively over swap.Earlier in the year these issuers were paying 100 or 105 basis points over swap for securitisation deals. For example, Westpac in February sold more than $900 million of a $1 billion RMBS deal at 100 basis points over one-month swap.ING Direct's last deal was in June, when it issued IDOL Series 2011-1. It paid 110 basis points over swap for the $748 million A1 tranche, which had an average life of 3.63 years.