What are the best ways on a sub-500 budget to test for mobile accessibility?

I am familiar with website accessibility at least in terms of WCAG 2.0, Section 508, etc. But I am currently designing a mobile app (cross-platform using React Native tools) and there does not seem to be many guidelines specifically for mobile apps either. In this case, what are the best ways, on a small (less than $500) budget, to test for mobile accessibility?

I am wondering if getting together a diverse set of testers and paying for their time would be better and more efficient in this regard, or would it be better to invest in other UX tools (sight tracking? Maps?). I will be testing using VoiceOver and TalkBack myself but I can't test all possible combinations of phones/tablets and flavors of Android, for example, let alone different combinations of assistive technology.