I have the 4, and my case was just about $90 at bestbuy a few months ago. Cheaper than buying a new iphone, though!
My son asked for one for Christmas (he has a 4s) and I purchased it....all $80 of it. Two days later its off his phone because he says he hates it and its the worst case ever. Now I'm stuck with it and he's out a gift, which is his own fault for not doing more research. He says after looking into it many people have the same issues he does. My point is you may wanna really sit down with her and research cases before investing in LifeProof.
What are his issues? When I did some reading on them, I noticed that responders to people with issues were telling them that they hadn't put the case on correctly. It's a tricky case to put on, and you have to invest some time in it to do it right.
I did the whole thing it tells me to. Put it together without the phone. Did the water test where you have it in water for a certain amount of time and make sure there are no leaks. Once it (and you, really) passes that test, make sure it's dry and put it on the phone.
I've taken it off a couple times (sometimes I just have to visit my pretty little iphone4, but then it looks so naked and vulnerable, the little glassy thing, that I can't even touch it unless I'm sitting on my mattress with pillows, LOL...I'm only *barely* exaggerating here), and once I had to re-do it within the hour. I hadn't smoothed the front of the case down as I was putting it on, and there was too much air in there, so the touchscreen wasn't as easy as it should be, and the sound on it was buzzy and difficult.
Took it apart, carefully of course, put it back together, voila, marvelous beautiful touchy good-sound-y phone again!
It's definitely worth it, though. Not a week after I got them, I was really distracted when my MIL went into the hospital for the 3rd time with another stroke, and I had put the phone down on top of my stuff. Went to pick up some of my stuff and the phone went flying across the hard hospital floor. Not a single problem at all with the case or phone.
DH makes fun of me b/c I still have the instructions sticker on the back of the phone, but I like having it there. Since it's a tricky case, but very important to do right, I don't mind having the instructions right there.