Check the cheap easy obvious stuff first. doubtful that the metal pipe as corroded, but if it has and its the pipe that goes through the block to the water pump
then it is easy to change but, Yes you have to remove the downpipes, then remove the sump. As well as a new pipe you will also need the "O" ring to seal the pipe in the water pump, and a sump gasket, new engine oil maybe filter while your there. Plus new coolant.
Sounds a daunting complicated job, but it really isn't that bad.
The hardest part will be getting your downpipes off if the studs/nuts are very badly corroded. if they are take your time be gentle loads of penetrating fluid, bit of heat helps if you have it.
then it is easy to change but, Yes you have to remove the downpipes, then remove the sump. As well as a new pipe you will also need the "O" ring to seal the pipe in the water pump, and a sump gasket, new engine oil maybe filter while your there. Plus new coolant.
Sounds a daunting complicated job, but it really isn't that bad.
The hardest part will be getting your downpipes off if the studs/nuts are very badly corroded. if they are take your time be gentle loads of penetrating fluid, bit of heat helps if you have it.