There are some apps that are available for free right now that you might be interested in checking out.
First, if you don’t have a camera app, besides the default one, Zitrr Camera is free right now. I just looked at it for the first time, and it has a lot of features including: different grids, a level, different shooting modes, anti shake, filters you can apply while shooting, and the ability to create mirrored images similar to mirrorgram.
LensLight is also free right now. If you like lens flares and bokeh, pick this one up. You can check out my review from a while back, here. I believe more lights/flares have been added since my review. Its worth a look for free.
Developer Dropico has a number of their apps available for free right now as well. If you like adding various effects to your images, or are interested in trying that out, you can save a lot of money by downloading these now. The downside to these apps is their size, which ranges from 49mb to 149mb. They do offer some cool effects though.