Rule 1 of con-pricing - start with your printing costs, and add to them.
Don't price below the printing cost. Just don't. If that means your prints are more expensive than the person standing next to you, then that's what they'll be. You need to consider your costs when you price your items; you want to break even, and you need to consider the cost of your table as well.
You don't want to sell things below the printing price. Sell at-cost if you absolutely must, but always try to add a little on the top.
Rule 2 - don't expect to sell out of everything at a con.
Some people do. Some people sell their entire stock and go home with all the money and none of the merchandise. Most people don't. Work hard to sell enough to cover the cost of your table, and then take whatever leftover stuff you have to sell and sell it online - or at the next con, or the one after that. It took me three or four cons to sell out of a print run of comics once, but that's okay, because I managed to cover the cost of my tabling at all those cons and earn a bit of profit on top, because I'd priced my comics properly.
I didn't break even on the printing costs until the last con, but you have to plan long-term for these things.
Rule 3 - price matters, but so does your sales-pitch.
So your prints are a bit more expensive than the person next to you - but your paper-quality is better. Your prints will last longer, and won't fade in the sun, and the colours look nicer, or whatever. Put that in your sales-pitch. Not the "I am so much better than the person over there" - I mean the "Look at the super-awesome quality of my prints! They will NOT fade and they will look great on your wall!"-bit. Talk yourself up, reach out to people, be friendly and engaging.
(note: don't talk yourself up by talking someone else down; being negative about other creators only to make yourself look better won't be doing you any favours - it will just make you look mean)