Let's do a little math.
Say I have a 60 page zine to print. I want high quality - full color interior, heavier paper, heavier card stock for cover with a matte finish. In a quantity of 400, I could print on Mixam.com for $1,144.50 or $2.86 per zine. (BTW, with black and white interior you can print for half that or less.)
Shipping. In the US I can probably get this anywhere for under a $1. Abroad it will cost more, but still probably under $2. [I've just had someone quote me a much higher price for international shipping. Not sure what method they were using, but I could be wrong here.] I'm going to estimate this at $3. We are probably going to pass this on the customer anyway so that people pay amounts relative to where they are. But let's include it for fun.
[Edit. Did some research. The real determiner here is media mail vs. first class mail. The latter is limited to 16 ounces and your zine should definitely be under that weight. So first class is cheaper and faster, so those are the rates I mentioned above. Media mail is quite a bit more. If you were sending a whole bunch to one place, then media mail would be best. But for single issues to individuals, go first class.]
Most retailers make around 40% (at best), so I am going to set my profit at $4 per unit. I will make more where shipping is ≤ $3, but Kickstarter or Patreon or whatever is going to take a cut. Let's call that 15%, and let's factor in another 10% waste for replacement copies, promo copies, etc.
To make $4 a zine, given all these factors, I would need to charge roughly $14 - printing, shipping materials, postage, waste, and distributor cuts.
On 400 zines, my profit would be more than $1600. Let's say that I'm paying myself and any artists, editors, etc. $20 an hour. That is 80 hours of work. If I spend fewer hours, I make more per hour. From personal experience, 80 hours isn't that far off what it would take to do 60 page zine. It might take more.
As my sales increase over 400, my profit increases, obviously. And it isn't even in scale because once I clear any payments to artists and such, it's all bills destined for my pocket (unless we are going splitzies on profit).
So there you have it. You can shave these numbers down of course, but I didn't include your gas to the post office or stuffing envelopes. I also forgot the cost of mailing labels (though we can assume just a few cents per) or any business cards you want to toss in.