Take good looking screenshots of your game on target device. You can hire experts for $5 to do it for you.

Hire an expert copy writer to write a good app store description. Approximate cost is around $20.

Get a Good press release written and published. There are many press release agencies. You should be able to find one for $50. 

Get a good game trailer made. A good trailer is worth 1000 words. This should cost around $20.

You may feel that the cost mentioned are too low. You can get good freelancers for this cost on Fiverr. 

Apart from the paid strategies you should also promote your game in these forums which are totally free.

r/freegames r/androidgaming r/gaming You need to have good Karma to promote on Reddit. But its totally worth it

If you have a good game then these sub-Reddits itself will boost it to the top charts. The users in these communities respond well to game links.

This is not a theory. We tested this strategy with a simple android game and a $100 budget. 

We spend the $100 dollars in a slightly different way, as we had inhouse graphics designer. You can read the results from the link below.