Wait a minute. You CAN afford a twin rating (and, presumably, twin hire/share/buying afterwards) but you can NOT afford an IR?
I know what I would do. Forget the twin rating for now and get the IR first. The IR is usable in a single engine aircraft, but a twin rating and the serious touring capability that comes with a twin, is not going to be very useful without an IR.
Furthermore, what's going to improve safety more: The extra engine or the extra knowledge and experience to fly in IMC, perform approaches to minima and so forth? Plus the ability to fly airways, under positive ATC control?