The CB-IR that prop is talking about is the competency based instrument rating. If you were to do the IMC you would be able to offset the dual training time against the time required for your subsequent IR. Once you have the IMC rating you could then fly as PIC in IMC which can also (up to a limit) be counted against the flying time for the IR when you go down the CB-ir route.
You'll probably find that even dual time in a 152 will be cheaper than a fnpt ii sim for the IR training. As you do the IMC you just need to be sure you're learning the sort of techniques and procedures that will help you through the IR later on rather than learning any bad habits which could be counter productive.
CAP 804 has info on the CB IR.