Yes it does. It is .20 cents more for a square envelope. You can look it up on usps.com. Right now it's .65 cents to mail a square envelope.
The cost of your mail is all about the weight of the package. the more that it weighs, the more it costs. The shape of the envelope is not going to change the price at all
"No, the cost of mailing a letter doesn't depend on the shape of the envelope but how much weight is actually inside the envelope. It's based on the weight."
$0.95 if it's a regular envelope; $1.50 if it bends easily and in a larger envelope; $2.12 if it's rigid or more than 1/4 in. thick and in a larger envelope.
The current postage cost for a USPS First Class Mail Letter (1 oz. ) is $0.49. Unless, the letter's weight is more than 1 oz. it is not more than that.
The cost would depend on the weight of the parcel. Big envelopes cost more than small envelopes of equal weight. You probably should go to your post office to mail this.
As long as the envelope doesn't weigh too much (If you're just mailing paper, then it probably doesn't) then no it doesn't cost more.
The postage rate to mail a 6x8 envelope in the United States as of 2014 is $0.44 if it is within the regulated weight. Additional costs may occur if it weighs more.
Yes, it is the same for the same weight. Both are considered 'oversized' mail or 'flats' and cost more than a normal business envelope. the current rate would be 88 cents for the first ounce and 17 cents for each additional ounce.
Letters sent by the royal mail with the Airmail service ( not you will need a special air mail envelope, these should be available from your local post office) will cost 56p to send to a destination outside of Europe. If the letter is heavier than 10g it may cost slightly more.
1 to 2 weeks or more
Hawaii is a US State so the postal rates are the same.
It depends on which country you are in and how big your envelope is. The bigger the envelope the more stamps you have to put on. ( that's in the UK)