Theres a link to a starter kit on here.
http://www.z4-forum.com/forum/viewtopic.php?f=15&t=63590
Or you can go mental and buy 3 million products if you like.
Have a look on detailingworld about the different stages and see how far you want to go.!
A half decent pressure washer should set you back £80-100 Argos have good deals sometimes & I think they take either club card or nectar points if you're a voucher whore