I sew, I sew quite well and win prizes at the county fairs around here. I can tell you that this fabric will be hard for you to find for less than $10-$20 per yard and it will be mail order only. If you supply the fabric, thread, and pattern and then pay her you will be spending well over $100. You will most likely be spending closer to $150 minimum.
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Here is an ebay place that has the fabric on sale, I would tell you to get at least 3 yards of it but you must have the exact pattern first, the dress pattern may be cut on the bias:
http://www.ebay.com/itm/Plain-Black-Stretch-Bengaline-Fab...
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I spent nearly an hour looking at vintage Vogue, Butterick, McCalls, and Simplicity patterns and there are none exactly like this dress. They start at the lowest around $25 and the average is more like $75, for just a basic dress like Mrs. Cleaver wore on Leave it to Beaver. The higher priced patterns, just the paper patterns that are $150 each. They are the bridal and prom ones, similar to this one but not exact.
Then you have to find black lace....as you can see, this is not a cheap adventure. The cost of the supplies to make this dress would make this dress easily several hundred dollars.
I say talk to her, pin down a cost of her services, then go find the supplies, EVERY ONE OF THEM, from the exact pattern you want, not one to be altered, but exactly what you want, to the black stretch fabric and black lace all the way to the thread, buttons or zipper too.
I think once you start finding the actual prices of stuff you will find buying this dress already made is a steal at $100.
I googled the fabric and found some cute sites for retro clothes, I love the top dress too. You have good taste but I think buying the dress already made up is the way to go here.
http://www.squidoo.com/pin-up-dresses