I think this is a horrible idea.
I'm 16, and I'll admit I'm spoiled. It all started out with things like this. It started out with small rewards for doing well in school. Then that turned into a gameboy color, into a gameboy advance, into a gameboy advance SP, into a nintendo DS, then into an iPod nano, into an iPod video, into an iPod touch, into a MacBook, into a MacBook Pro, into an iPhone, into an iPhone 3GS, into an iPhone 5. You're just digging yourself into a hole and you'll end up with a daughter that will want every goddamn thing in the world.
My parents were against me getting an iPhone, saying that "if I got one now, there's nothing left to want in the future." I think they were right.
And for god's sake, she's 5. What does she need an iPad for? Get her a doll as the high tier reward and a sticker as the low tier reward. You've screwed up the scale. Especially since you lost your job, you need to get a hold on your financial situation for now and the future.
I know a bunch of girls my age who started out like your daughter with parents like you. Nobody likes them, because if they don't get their way, they WILL do everything they can to get it. This translates to objects, friends, and even sex.
I am smart, I have a 3.8 GPA and excel in the sciences. If you're willing to sacrifice her attitude for success, then so be it. I can't make you do anything, but just understand that when you start threads like these online, you are attracting criticism. If you didn't want criticism, then you should not have started this thread.
Just my 2 cents.