The latest iPad 2's that are being produced don't have the iPad 2 power/volume flex. They have the iPad 3 power/volume flex. This flex obviously looks different. Check for damage to the flex cable and check that all connections are seated properly.
It's simple supply and demand. Apple can't make the iPhone fast enough and haven't even launched in all countries yet. The price will come down as soon as Apple can easily keep up with demand. The new screens also use new technology to be produced. This new technology means that no one can make copy versions that are much cheaper either.
For a full earpiece speaker repair you should remove the front screen and replace the 3 piece earpiece speaker mesh. It is available from HERE The proximity sensor comes as part of the proximity, power/lock flex cable. Is it possible that you've damaged this when changing the earpiece speaker over? The camera light not working - do you mean the LED flash for the rear camera?
The iPhone 4S has 2 microphones. One comes as part of the dock connector and is the main microphone. The secondary microphone acts as a 'noise cancelling' mic when the phones held to your ear and acts as the main microphone when your phone is on speakerphone and when recording videos. It sounds like you need to replace the secondary microphone. This comes as part of the headphone jack flex on the iPhone 4S. PART GUIDE The iPhone 4S is still under its 12 month warranty. I would highly recommend using Apple to honour this warrant before carrying out the repair yourself.
First obvious port of call is to replace the dock connector - however you've verified that from a hardware point the microphone works so I don't think this is your problem. It sounds like the audio decoder. This is a fairly common problem with the 4 and 4S. Apples policy is to swap the phone out for a replacement but that's useless for phones over 12 months old. If your iPhone is under 12 months old take it straight to your nearest apple store. Symptoms are exactly as you've described. Sometimes the problem is intermittent whereby it will work for sometimes days without trouble but then will randomly mute for no apparent reason. It will then sometimes work from time to time but eventually getting worse and worse to the point that each and every call is the same. Without some serious soldering skills your best off looking for someone to do it for you. I'm not aloud to advertise services on here but if you message me I can help. If not you please look for an experienced, reputable iPhone repair company - its...
The original replacement iPad 2 and iPad 3 digitisers with the original flex cables are designed in a way that the flex cable bends around the inside of the back housing. Take a good look as you are removing the original screen and you will see how it arcs. When you fit the new digitiser the start of the flex cable has a firm part which is there to poke in between the LCD and back housing. The cheaper replacement digitisers lack this 'firm' part of the flex cable and are really hard to get the flex cable to shape as necessary for the glass to lay flat. The original adhesive to fit the glass comes black in colour. You should never need any more adhesive than the black double sided adhesive.