etsy cards/printing your own - is this right?

i know when you have a custom card makde from some place like etsy, etc. it was suggested to go to costco. however, when i go on their site, i don't see a 5x7 option WITH envelopes. that's nuts.

i got some suggestions for mpix.
http://www.mpix.com/Product.aspx/postcards

is that right? the 5x7 postcard for a regular card? how is this company as far as shipping goes?

Re: etsy cards/printing your own - is this right?

i think.....costco has their own size....if you want to use them you have to have the etsy seller make them that custom size (can't remember what exactly it is right now)