Tablets are really hard to use (tablets like iPad or even Android) for freehand drawing and painting. I'd recommend the good o'l graphics tablet. It'll take some time to get used to it, but it gives you greater results.
I'd recommend a Monoprice in the case you can't afford/find one that you're asking for--it doesn't have the on screen bit you're asking for, but the one I have was about $40, without the extra nibs and pen that I bought. [link]