Congrats on your engagement!
I used to work at David's Bridal, and they offer tons of styles at reasonable prices, and can add sleeves & straps to any strapless style. The ladies in the alts department really know what they're doing, and if you let them know how you'd like the straps placed, I'm sure they'd be able to help. When you go (to any bridal shop) take this picture with you and the ladies will be able to show you what they have in a similar style. It's a lot easier than trying to describe a white dress. And what UntouchableFace said about trying on lots of styles is great advice. Here is the website of their sleeve options: http://www.davidsbridal.com/accessory_return_sleeves.jsp
As for having a dress made for you, the price will vary based on the quality of the fabrics used, how quickly you need it made, etc, etc. And your return options if you're dissatisfied are next to zero. If you go this route, you'll want to interview your stitcher just the same way you would a candidate for any job - ask to see pictures of their previous work, especially wedding gowns, agree on a budget up-front, and get everything in writing. I've seen a lot of people try to save money on their wedding/bridesmades dress by having someone they know do the alts, only to be so disappointed in the results that it actually ruins the friendship.
If you live near a college, you might see if they have a theater program and speak to a professor there. Costume designers sew very well, and are generally used to a freelance type environment. Furthermore, they should all have portfolios to show you. If they don't have anyone qualified, they might be able to point you in the right direction.
My final caution is this: Don't fall so in love with this dress that nothing else will ever do. You want to focus on the silhouette and how it flatters your natural shape. Just like wearing makeup, the dress should enhance your natural beauty, not draw attention away from it. And remember one thing above all: No matter what else happens, at the end of the day, you're still married, and that's really the point.
I hope you have a wonderful time planning, celebrating, and starting your new life.