Hun, it may not be much help here and I see you already have a bunch of great advise, but I cannot help adding my $.02 ;)
I found my MOH's dress on eBay for $21.21 (with shipping) Lots of people there buy stock from out-of-business dress shops and sell them for a profit. (When this one came, it had a $180 price tag still attached) Its common now to have each girl or just the MOH in a different dress... though it may be the same color. Maybe you could find a similar dress on eBay and stand out slightly as MOH?
Netbride.com is another place I looked into. They are a brick and mortar store that sells/ships directly to you, cheaper. My own dress was $630 in the salon, Netbride sold it to me for $371. They have bridesmaid dress there too, s you might be able to get the same dress; much cheaper. (you can email them for a free quote)
HTH :D