unity3d expirience 5 years, mobile platforms delivery a lot, similar project done. have the android device and all latest tools to build and fix and debug.
i can provide more details after connect with you. there is a lot basically, but depends on the sources itself ofcourse. if errors are not commited no plugin renewal and version backwards uncapompability should be pretty easy. tho sometimes could take months, nothing particaular can be said before looking into the code. so the bid is floating really. 150 bucks is like 3 days tops, which is considered as fixing small bugs, build and deploy if needed