If the phone is a 4 / 4s then to replace the screen and the "lock" button (do you mean the mute or the power button ?) you're looking at about £60 for the two, supplied and fitted.
The WiFi problem is usually caused either by a software fault (you'd need to back it up and update it) or, and it's very common, the chip that controls the WiFi on the board has gone down.
Apple say its rare, had three of them in this week alone, so it's a common rarity.
Solutions to fix it vary, but with the other faults you're getting close to an exchange price so I'd back all you pics up and reload them on to a nice shiny new one.