Thanks for all the comments 
In terms of getting a good price, shop around. Bmw are desperate to meet sales targets especially on the z4. Stick to the price you want to pay and if they dont agree to it walk away. One of them will eventually call back!
Also, target a larger Bmw dealer as they can afford to discount more which I found out with my car. Whatever the finance example and dealer contribution is on the website, you can always get them to reduce it at an actual dealership.
In terms of getting a good price, shop around. Bmw are desperate to meet sales targets especially on the z4. Stick to the price you want to pay and if they dont agree to it walk away. One of them will eventually call back!
Also, target a larger Bmw dealer as they can afford to discount more which I found out with my car. Whatever the finance example and dealer contribution is on the website, you can always get them to reduce it at an actual dealership.