When I worked in bridal we carried this dress by Sophia Tolli;
I believe it was around $2,300, but it could have been a little more or less. It all depends on the designer you choose. You could also always ask if the seamstress you have doing alterations could make something to add to a dress, depending or the brand and your location, that could be cheaper! Let me know if you have any more questions!
Thank you! I am worried I won't be able to find a lot of this style in store, and pretty much have my heart set on it. Adding a skirt to an existing dress wasn't something I considered, so that is very helpful.