Even if the invitation specifically states black tie, you are not required to rent a tux. With the right shirt/tie combo and accessories, you can wear a black suit you already own.
You could always purchase a tuxedo shirt, complete with traditional pintucks (the pleats down the front you probably call ruffles) and/or wing collar (the collar meant for a bow tie), but any pristine white shirt will suffice.
For a formal event, French cuffs are preferred.
Your tie should be black, white or silver. It doesn’t have to be a solid color, but you don’t want anything too flashy. (Never outshine the bride and groom.)
A pocket silk is the perfect finishing touch and freshly polished, shined black shoes are a must.
Next: Getting a tux?