Not sure if this is the same as an 'envelope gift bag', but it sure looks the same as a purse shaped stationary holder I have made a number of times using the following link, and then just adding the handles separately. You can use a manila envelope if the size is suitable for your cards & envelopes, or make a custom envelope first and then follow the same instructions. I find it easier to make an envelope myself first because then I can stamp the whole sheet while it is still flat, before folding into an envelope shape. Hope this makes sense ...! LOL
http://raft.net/ideas/Envelope%20Gift%20Bag.pdf
You can also use this template from Mirkwood, adjust the size and leave the top flap off to have a purse shape, then add handles:
http://www.ruthannzaroff.com/mirkwoo.../portfolio.htm