firstly is it the 185i or 215i V8?
because you'll need a stroker cam if its the latter...anyway, C.O.M.E. racing offer a new cam, lifters and chip package for just under a grand for the unstroked vn-vs V8...i couldnt say how much it offers in the way of improvement (as i dont have a V8,lol.) but you've got a rought idea of price.