If, like some, you are on a tight budget then your best investment is a black Argyll jacket and two black waistcoats-- one 3 button (like those worn with a PC) and the other a standard six button affair.

Six-button waistcoat + Argyll, & four-in-hand tie = day wear/dressy evening wear = suit and tie.
Three-button waistcoat + Argyll & bow tie = formal evening wear = tuxedo.

So there you have it, the basic formula for being well-dressed on a budget:

[1(Argyll Jacket) + 2(waistcoats)] - (white socks) = 1 Well Dressed Gentleman.