To be honest, if you're low on cash I would forget it for now. You will, I repeat, will spend more money than you envisaged. Take your first estimate and add 30-50%. If you're tight on money you will find the training more stressful which will inevitably spoil your enjoyment of the training and, more importantly, distract you from your primary aim of gaining your licence. You can do some of the training for the IR in the US but the test itself needs to be taken in the UK. Furthermore, US approaches, airspace and terminology are quite different from the UK so there is inevitably a degree of retraining. Believe me, I know, I have both FAA and JAA IRs.