Shipping Rate Question

[MLPlyte]

I'm sorry if this has been asked before, but I'm making my first real "For Sale" thread and I want to be sure I'm quoting shipping properly.
If I ship Priority Mail, it doesn't matter the weight of the item? Is that correct? So say a medium sized bubble envelope with one doll in it would be $6.95, and a large bubbles envelope with 2-3 dolls in it would also be $6.95. Or have I completely misunderstood the USPS website and the Shipping thread stickied at the top?
Also, would it be better to use the Priority Mail boxes and envelopes I see in the Post Office? I've heard they are free - is that right?
I really appreciate any help with this. My postal workers are very patient but also very busy and I don't want to go in there and hold up the lines trying to understand this.

[ponylady]

I am in the middle of updating our shipping page so please do not use that for reference right now.  USPS raised their prices considerably on Jan. 27th so any info on that page is outdated.

I first would suggest to make sure you have a Postal scale to weigh your items.  Then educate yourself a bit with the links I am going to post below. The first one is USPS's postal calculater, in which you can enter the zip code it is going to and the weight. It then provides the prices for all mailing options. It will also give you calculated shipping for International sales.

 http://postcalc.usps.com/

 https://www.usps.com/ship/service-chart.htm

http://www.stamps.com/usps/postage-rate-increase/

The weight is going to matter depending which service you use.  I believe Priority does not change as frequently in price until you go over 13 ounces. First Class will though, although this is the cheapest method of shipping and now provides tracking.

As far as free boxes, yes USPS provides them free of charge for Priority shipping.