Google Ads for android app

I run an Android music app that offers tiered subscription plans, and I want a data-driven Google Ads campaign for play store built around the new Sales Goal objective. Downloads are great, but the real measure of success for me is the volume and cost-efficiency of completed subscription check-outs... (Budget: $30 - $250 USD, Jobs: A/B Testing, Android, Android App Development, Conversion Rate Optimization, Digital Marketing, Google Ads, Google Adwords, Google Analytics, Internet Marketing, Search Engine Marketing)