Dave,
Nice try but 2 minor problems.
Firstly, most IR's have a significant chunk (up to 35 hours) in a sim, which do not count as part of the 150 flying hours to start the CPL.
Likewise, you need 70 hours P1 to gain a MEP rating and 100 hours P1 for CPL licence issue.
The harsh reality is that your ability will make far more difference to your costings than the order of the courses. If £1000 extra puts you over budget such that you'll run out of cash and won't be able to complete, then think very long and hard. 1 hour in a twin for additional training is over £300 at most schools and retaking CPL or IR flight tests doesn't bear thinking about. It's worth pointing out that the ME IR is far far more demanding than the CPL, so most people choose to complete the CPL first to gain the maximum training and experience.
Regards,
Obs