So, you're doing the job of the finance company; that doesn't change the principle that, on certain cars (including BMW's) the expectation of certain options (such as leather and navigation) will have a profound effect on RV - debit card, cash, finance, lease - the mode of finance doesn't change anything. The initial outlay at point of purchase will be partially recovered at time of sale - the difference is the actual cost to you over the duration of ownership.
Gone but not forgotten:
325i M Sport (E92), Black Sapphire, Coral Red Dakota, 19" 225's, Seat Heating, 6FL and de-badge
Replaced by 6.2 litres of AMG powered C class.