Hey there,
Currenly I'm not living in in Istanbul, but my intention is already different a little bit actually :)
As an Android power user and phone-tech enthusiast, I really would love to participate you user testing project as a participant. I don't believe distances would be a problem for giving feedback if that's wont be done face to face. And for testing a new device, I can even compansate back and forth shipping costs if you consider adding me as a tester.
On the other hand, If you decide the location of the coordinator is doesn't have to be in İstanbul, I can also happily help you and gather people from Ankara and İstanbul mixed. Unfortunately I cannot promise about only İstanbul.
I've also done a few recruitment projects before. The last one was gathering Scania truckers and prepare a file for a documentary done by Scania. I believe we can discuss the other details if istanbul is not mandatory dor coordinator. But I believe it's not as a participant.
Looking forward to hear back from you, have a great day :)
Edit: You can consider the price point as a placeholder. It can be discussed and be found a mutual point.