I will try to not give you such a spammy response like the other answer here. Although I do agree, you don't really provide any information.
When it comes to marketing you need to realize that marketing in itself is not advertising - why do you think you need money for marketing? You definitely need it for advertising but depending on your app and your users you might have a world of opportunity to reach more and get more from these downloads than you might realize.

My name is Humberto Valle, and I am strategic competitive marketer and have been helping startups grow from zero to millions of dollars for about 10 years now. I run a marketing agency and do consulting calls for fun. If you want more direct clarity - send me a message and I will be of as much help as possible.