What kind of format are you using for your scripts?
If you're using FDX (industry standard), then you could use "Storyist" (my favourite), "Scripts Pro" or "Screenplay".
I wrote a Squidoo lens where I give in depth reviews of all the screenplay apps for iPad, if you're interested: Best Screenplay Apps for iPad
Scripts Pro is now pretty good after it got a major update. You won't get any power features from Final Draft but for just writing it does the job well.
When I first started work in the industry.. Final Draft was the standard.... But way too expensive for some... a lot actually... Even their apps...
I find myself using Celtx (free on Mac/Windows) and they have an App for iPhone and iPad... You can work on the same screenplay on multiple devices, which I love (syncs amazingly). The app cost me like... 5 bucks, but I think it got cheaper since then... It's probably my favorite filmmaking app.. I can't decide if I use it more on my computer or iPad... I have sausage fingers, so it's near impossible to type on an iPhone (for me at least .