I'm making $200/mo on average from one iPhone app. It took me a month to build it a year ago and sales have remained stable, except for one $800 month when I go

I'm making $200/mo on average from one iPhone app. It took me a month to build it a year ago and sales have remained stable, except for one $800 month when I got featured in a popular newsletter. I'm currently polishing up an iPad version and will experiment with increasing the price when it goes Universal.