In fact, 2 mates asked me the question while I was crafting some stuff for them and it seemed legit for them because while I craft for them, I don't craft for me. But this idea never crossed my mind. If yes, how much ?
Charge Them In Favours
When you have to choose between building relationships between characters (story) and adding numbers to your sheet, you should always choose the relationships. Have opinions. Craft a pair of magical boots for the rogue, but later ask him to steal some embarrassing blackmail photos - make a magical shield for the fighter, and later when he resists a dragon's breath using it and helps you up from where the breath blew you into the wall, mutter something about the shield being useful and him paying back the time you spent on it. Charge the monk double cause you hate him, and charge the druid nothing at all because you were raised to venerate priests, even weird priests of nature.
I.e. use the crafting to accentuate your character. As a crafter, you can be either Iron Man or you can be that guy John Constantine goes to to get his weird magical crossbows or whatever. Either way, the stuff you produce is a big part of your character - you spent feats on that, bro. If it doesn't add to your interaction, your roleplaying, who you are - then you've wasted those feats. Roleplaying is about story. Sure, maximize your party's stats while you're at it - but this is a win-win. You get to do both, and so you should.
Don't think about what you 'should' do, think about what you will do to make the game awesome.
As much -- or as little -- as you want.
I've been in multiple games where this has come up. Sometimes the crafting character charges a sum comparable to market value (making a tidy profit for his time); other characters charge less than market value but above their cost (in which case both crafter and craftee in effect profit from the transaction); most seem to charge only their own costs. I've even seen one or two that didn't even charge their own costs for the service, reasoning that -- as a member of the party -- they benefit just as much from the recipient having the item. (There was also one who demanded above-market prices for his services, but he was The Party Jerk and demanded such a high price specifically because he didn't really want to do it.)
It really depends on how you want to play your character. A Ferengi-type interested in maximum profit would lean toward charging market value (which may still benefit the recipient, e.g. if the item isn't readily available); a Vow of Poverty candidate would lean toward charging only cost, or nothing at all. So, ultimately, the only possible answer here is: Whatever you want to charge.
I wouldn't charge them anything for the actual crafting (your time), but any resources you have to use to create their item should come from them. And remember: anything you are producing "for them" is really going to benefit you in the long run, as a member of their party.