Intermittent backlight - bad ambient light sensor?

I dropped my phone in the toilet about five months ago. I kept it in an airtight canister full of rice for four days and I live in Salt Lake where the climate is pretty dry anyway. I turned it on after four days and the only thing that seemed not to be working is the backlight. The touch screen is fine, the speaker is a little tinnier than before, the volume buttons work, the touch screen works. If I used the phone outdoors in bright sunlight I could sort of see the screen, or if I shined a flashlight up to it I could see it. The LCD seemed fine, all my apps worked, my data was intact, etc.

I got really bummed, but didn't really have the money at the time to buy a new phone or attempt a repair, so I started using a cheap Nokia (an AT&T Go Phone) with my SIM card.

About a month ago, though, I needed some information that I knew was only on my iPhone, so I charged it up and turned it on and held it up to a lamp so I could read the screen. After fiddling with it for about two or three minutes, BOOM, the backlight just comes on! I turned it off and back on several times and pinched myself to make sure I wasn't just dreaming. Then I got really excited and stuck my SIM card back in and started using it. Later that day I turned the phone on outdoors and the backlight didn't come on. I was about to give up on it all over again, but then turned it on later in the day indoors and the backlight worked again. This is when it dawned on me, the problem must not be with the backlight at all, but with the ambient light sensor. So I switched it off in preferences and ever since then the phone has worked fine.

Until today, that is. As I was getting out of my car this morning I dropped my phone maybe a foot and a half off the ground onto cement. There is no visible damage to the phone (screen is still intact, etc.) but the backlight wouldn't come on again. I brought the phone inside, turned it on and off several times, no change, set it down and walked away. Few minutes later picked it up again and the backlight comes on the moment I turn it on. I wipe my forehead, whew, and continue using my phone. Later today I'm walking around outside and I turn my phone on and the backlight doesn't come on again. Arg. Now it's been several hours and no matter what I try I still can't get the backlight to come on again.

So, here's my question. I'm 99% positive my backlight is fine and it's that pesky ambient light sensor that's causing the problem, even though I've double-checked and it is disabled in the software. In your professional opinions, oh wise iFixit users, is there any way to disable the ambient light sensor for good? Can I open up my case and just unplug the ambient light sensor somehow? Would it be better to replace it? If so, is it expensive to replace? What should I do? If this isn't super cheap or free to fix, I plan to go back to my Go Phone until 4th-gen iPhone comes out. I'm going to buy one of those whether I can fix my 3G or not. Thanks.