Where can I get a cheap iPhone 6/6s?

I have an iPhone 4s right now, and on Thursday I'm going to get a new phone. I guess iPhone 5s would be alright, but I would much prefer a 6 or a 6s. Please if someone could tell me how I can get a cheap iPhone 6/6s thank you in advance! (Refurbished is fine)

Replaced iPhone 6 screen and now the screen goes black and lock buttons unresponsive?

I just had my iPhone 6 screen replaced at a local phone repair shop. The shop is reputable in comparison to other local repair shops and therefore I went with it.

The screen took around 20 minutes to replace and it was fine the first few minutes after. I then locked the phone and went to unlock it, and the screen was blank. The phone repair man fiddled with it for a few minutes and again, it was fine. I went to the car to drive home and again, the screen was black and the lock buttons were unresponsive. By the time I arrived home again, it was working. And then I locked it again and it went blank.

Why is this happening? What can I do to fix it?

Instagram won't let me add accounts or log out?

I go to my settings and it won't go bast the "about" section. No blue links. I have to delete the instagram app and get it back to change accounts. I only have 3 accounts so none over 5. The links in my settings go down to "open source libraries" and nothing past that! The accounts aren't banned. I don't post anything bad. What can I do?! (I got a new phone but I set up icloud correctly and went to the store for them to do it. I don't think it's anything to do with that.) I have an Iphone 5.