You could be happy for 100 units sold in a month maybe, and i say maybe, because you make the game yourself and try to cover all things alone but for a small company, always considered indie, like mine 1000 units per month do not cover our costs.
What i mean is simple, what is good for someone maybe isn't for others. To make a game, and for me make a game mean a full game with:
Intro,
Menu,
level selection
a good amount of levels
end sequence
Musics and sound effects for each different thing.
For musics i mean something unique, ordered to a professional composer not downloaded from a free and public domain website.
A decent graphics quality.
Graphics i mean made in 2d or 3d, depend on the game, by peoples who has a minimum experience on how to make something for a game not free set available for everyone in the web.
I have nothing with peoples who take gfx and musics from the web but i can't do it, when i want to make a game i want to use my gfx not something that everyone can use.
All this have a cost and for sure i can't cover for 700$ x month. 1k sold at 0.99$ (if we are selling for a fixed price) generate a revenue of 700$ a month and for sure for a single people who has the ability to create all himself is good but for us, not less than 3 peoples, is bad.
Our 1st game the 1st month after his release had a bit more than 700 units, it was the best month, the game still sell few units a day and considering it is not visible in any leaderboard or website is a good thing. The game in total after 1 and half year sold in iOS, Bada, Android(Samsung App Store), Amazon, nearly 10k units, with a revenue of less than $7k that are the money i spend in 1 and half month, maybe 2 months, to take care my company.
Honestly i don't want to sell 1k unit x day but i would like to have a decent amount to continue to create games.
I read an interview with a guy who has opened his own company, he has a very big experience in AAA games like Assassin's Creed and other similar games, he knows how to work with a team of 100 peoples but he choose to change his job and tried to build his own company. In his interview he simply said that a new game with a good marketing and if at his release is in the New And Noteworthy can have am amount of downloads of 6k the 1st day. He also said their 1st game made in 6 months about $145k with a development cost equal to a bit more of euro 100k, in 6 months he hasn't recovered the investment yet but he was happy for the 1st experience.
The euro 100k cover not only the development but also a bit of marketing, 25%, trip to GDC, E3 and other places to speak with peoples from press and website to try everything to make his game visible. He also added that the best to sell a game is to have afriend in Apple
He is a guy well integrated in the industry and with all this he has some difficulties. There are exceptions for sure, there are peoples that with a single game made millions but is not the base is just an exception.
At the moment we are making 2 games using AppGameKit and 1 has been sent to Apple for approval for Mac OSX, i don't know how many units it will sell when will be released but for sure i hope will be good.
I can share the downloads when the game will be released and i hope there will be some.
http://www.7ravenstudios.com
https://www.facebook.com/pages/7-Raven-Studios/102567824318?ref=hl
https://www.facebook.com/groups/391126020940838/