How much should I sell my used iPhone 5 for?

I currently have a 64GB iPhone 5. It has one or two tiny scratches on the outside edge of the phone (which would be covered with a case anyway). The screen is in perfect condition, and everything else works fine, but the one "big" issue with it is that the volume buttons on the side of the phone no longer work (it's never been much of a problem to me though). Otherwise it's totally fine.

As I'm planning on getting the iPhone 6 sometime this fall, my boyfriend's brother has expressed an interest in buying my old phone from me when I get my new one. I'm at a total loss about how much to ask for it.

Given our relationship and the less-than-perfect condition of the phone, what do you guys think?

Prices vary worldwide and you made no mention where you are.

But they're popular models and large memory capacity versions always attract a price premium. Just stick it on ebay and describe it honestly and there will be sufficient buyer competition to ensure you get the best possible price for your faulty phone. But you'll only get the best price by getting the fault fixed as buyers will treat a faulty phone as a bit of a gamble.

If you don't want to sell it to a stranger on ebay, then use the completed listings feature to search for what identical models to yours have been selling for and then deduct around 150% of the cost of repair. It's up to you whether you want to then give your boyfriends brother any further discount, but discounts are less money for you, and are identical to just handing him money for nothing.

If i were you i would get myself to an apple store and tell them about the volume buttons, i had the exact same problem with my iphone 5 64gb. I went to an apple shop last week to get the buttons fixed and i was happy to pay the $200.
I explained to them that i had taken very good care of my phone and i wasn't sure why the buttons werent working. They could see it was in excellent condition for a two year old phone and so they replaced my phone with a brand new iphone 5 64gb and diddnt charge me anything. Apple have excellent customer service and i think because the new iphone is released soon they don't mind giving out iphone 5 if they belive you and can see it isn't your fault. Also my iphone was not under warranty.

Brand new iphone 5 i would charge $400+
As it is now with broken buttons $180+

Goodluck!

i probably should add that i'm from Australia, iphone 5 64gb here when they came out were $1000. But i know prices vary around the world so maybe 1/3 to 1/2 of what you paid as a rough idea.