I am impressed that people have completed their training for a figure of around GBP35K. Although I did not keep a full record of my training, I've estimated that I spent around GBP55k.
If I had my time again, I would definitely do my CPL in the US as it gives you very little value and is a very out-dated course. In addition, doing the CPL in the UK is exactly how it was when I did my PPL: the number of days lost to bad weather is no different. And if your luck is like mine, you will have a prolonged period of time drinking tea and wishing you had done it in the US. One chap at my school in the UK had to wait 3 weeks for the right weather just to sit his flight exam. This was on top of a lengthy delay in completing his course. My own course overran by three weeks. So that was 15 days extra in the B&B, plus all that additional traveling to and from my home each weekend to the school, only to jump in the car on the Friday evening after a week of no flying.
Do your IR in the UK. No question.
As for budgets, always remember things such as costs of traveling to the airfields, taxis from airports when going abroad, and the fact that if you are going away for long periods of time, it is unreasonable to think that you will sit in your motel not spending any money when not flying. You will need some money for 'entertainment' and unforeseen activities.
I always added a 10% figure to my budgets as a minimum, since things are always more expensive than you think they will be. Plus, most will go over by 3-5 hrs on their IR, and many get partials, which requires additional funding. The last thing you want to worry about is finances when you are already under pressure in your IR.