Please, need help with fuel pump!

Hi, I ve been having some cold start problems recenlty with my mazda astina. I had my mechanic to check the fuel pressure overnight and he found a split fuel hose..so that was fixed.Car still needs long cranking time to start. The next day, fuel pressure was down to almost zero. Im wondering whether my check valve is gone because its not retaining any pressure overnight. Please help me out because the mechanic told me it would cost au$400 to change the pump. he checked the fuel pressure regulator and that was fine. Is there any particular brand that i should use. I m not buying the mazda one because that would cost me around au$800 just for the pump.
thanks guys.