If you cannot do the mutual flying with another trainee it will have to be done with an instructor i.e. you pay dual rates vs solo hire of the aircraft. Depending on the school this could add anywhere between $50-$100 per hour to the cost of the rating, therefore an additional $1000-$2000.
Working 5 days per week then completing the FIR on weekends is hard work, trust me! You will be fatigued and your partner will be on the verge of leaving you unless they are very supportive. If possible try to take some annual leave from your work, even if it is just a week or two. This will help with the timeline and improve your output as a trainee. The flying component is very small - there is a lot of hard work in preparing and presenting briefings.
Any school that gives you a book to cover PMI/IPM isn't complying with the CAOs - CASA would love to find out about them!