IL/WI Wedding & Salsa Style Wedding Dress?

Hello! I`m 26 & my fiance and I are trying to decide the specifics of our wedding. We want to be married outside with our friends and family surrounding us either in the Chicago or Milwaukee area, but we`re paying for it ourselves & it needs to be not-so-incredibly expensive...(any ideas?) Also, I am envisioning myself in a low-cut square-necked boddice dress that buttons or ties up the back and has a knee-length tango or salsa style skirt. I`d also like to be able to add different colors of fabric to the skirt at the reception to match the gerber daisies and give the dress a little "fun" side to it. One problem... I have NO idea what-so-ever as to where find a dress of this sort. Any ideas?