A good first step, and one that many people do not heed, is to think about yourself.
Are you fit enough to go rallying? A clubbie event on a disused airfield may not require the stamina of a marathon runner, but a reasonable level of fitness and upper body strength is always a good idea. If you are looking to do bigger and longer event, you will need to be moderately fit. And that's not just about going down the gym twice a week. Take a long hard look at your diet, drinking and smoking. We're not suggesting you become a teetotal lentil-muncher, but a sensible approach is needed.
The logical way to improve your performance is to enlist the services of a rally school and/or a driver coach. Just like any sport, there are professional coaches who can seriously help you improve your performance, and money spent with a good coach is likely to bring a much better reward than spending money on the car.