Harry: "But Hagrid. How am I going to pay for all of this? I haven't any money."
Hagrid: "Well there's your money, Harry! Gringotts, the wizard bank! Ain't no safer place. Not one. Except perhaps Hogwarts."
Before you can go shopping in Diagon Alley, you will need to stop into Gringotts wizarding bank to collect a few knuts, sickles and galleons.
Gringotts wizarding bank is the only bank of the wizarding world, and is owned by goblins. Speaking of which, there is one looking over vault 687 now guarding Mr Potters spare key.
If you are polite, he may let you have a sneak peek into the vault and borrow a coin or two. Just make sure he is back to his guarding post after relocking the vault.