Hi there, based on my experience, here are some effective and cheap user acquisition methods for you.
Buy keyword Search Installs - Boost App Ranking in the App Stores
Data shows that over 65% users download an app by searching keyword in the app stores, and most of them just browsing the top 20 qpps - the higher your app rank, the greater chance that your app will be downloaded. App store optmization is a good way to boost app ranking, but it's a long term project, for a new app, the best promotion time is the first two weeks, then you should grasp the gold time to promote your app. Buy keyword search installs can boost your app ranking in 8~10 hours, really worth to have a try. Highly recommend.
Buy App Reviews to Increase the Download Rates
70% users will see at least one app review, 95% users will take the app reviews as one of the most important reference factors to judge the app(especially for a new app), but only 42% users will use their own judgment on the quality of the app. Then, for a new app, buy app reviews is a great user aquisition method.
Before launch, you should optimize the following aspects to increase the download rates:
Hope those methods are useful to you.