Dear Customer,
I had been working as a software tester in large international corporation (Epam),
and I can say the following:
1. The code review is not a replacement for a manual testing on real devices
2. A testing on devices must begin with defying of use cases, how this software will be used, with identifying of user's roles (who and how will be using your software).
3. Testing your app on 50 real devices?
I have to contact the sellers of the devices, I don't think the seller of the device will agree to test something for less than $20 per device, plus I have to spend time and fuel to find proper devices.
So, the average budget of test plan test cases and use cases creation is $500.
As for the usage of "50 real devices" + a time spent to find where to test them, time spent on negotiations with these device sellers $2000 -3000
So, the average budget for this project is approx $500-$3500.
For $100 you'll get a low quality, semi- or fully-faked result from someone, you'll never get even a 90% use case and test case coverage.