According to your budget, here are some appropriate promotion methods for you.
Offer discounts
If you are working with in-app purchases, offer them at cheaper prices on certain days, and let your users know via push notifications or your email newsletter.
Host a giveaway
You can create special prizes and raffle them away to those who share your app, post about you, or complete other tasks.
Offer free trials
If your app is paid, offer a free trial to collect potential user information.
Give out promo codes
Users are much more likely to engage if they can save some money.
Influencer Sharing
The same as celebrity effect.Leveraging the power of influencers can be the best way to drive mass amounts of traffic to your mobile. You can find a list of relevant influencers in your mobile app’ space on the internet.
Buy app ratings
Only 15% users would like to download those apps with 2 ratings, and 50% users would like to download those 3 rating apps. However, 94% users would like to download those 4-5 rating apps.
Buy positive reviews
Generally speaking, people prefer to donwload an app which has much more positive reviews. 70% users will see at least one app review, 75% users will take the app reviews as one of the most important reference factors to judge the app, but only 42% users will use their own judgment on the quality of the app.
App store optimization
App store optimization (ASO) is, at it’s core, search engine optimization (SEO) for the Google Play and App Store. Just like search engine optimization, app store optimization focuses on keyword relevance, search relevance and the keyword density in your description.
Host a contest
Tell your audience to complete a certain task and tag themselves with contest-specific hashtags on social media in order to follow the development. Reward the winners publically.
Besides these economical promotion ways, there still are some free ways to promote your app, such as email marketing, post on forums, social meida, blogs, etc.