The banks valuation may have been carried out using "hometrack" as a guide which is something that lenders and estate agents use. I compiles local area demographics with purchase prices and recent remortgage values.
When I worked for a high street bank they would try to sell a repossessed house as near to full market value as possible. They would recoup their legal expenses, the full outstanding mortgage and pass any left over to the borrower. Todays financial climate is a little different and the banks objective will be. They will want to sell the property quickly and cover their costs. It may help you if you can find out how much the bank needs to cover costs. Some times a bank will accept less for the property than is actually owed and the remaining balance will become and unsecured loan for the borrower.
As far as financing the deal, once your at the mortgage stage it is sometimes good to use a mortgage advisor who deals directly with a packager so that he can convey exactly what kind of deal is being sought, the packager can then pull the necessary strings for valuations.
I do know that if a property is undervalued, it can be very difficult to get minds changed on the valuation.
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