BMW DEALER NORTH

Advice required....

I know I should not have to ask but just in case I am unreasonable, please say what you think:

So, saw a bike at a BMW Dealer, told the salesman it had everything I wanted except the Audio System (R1200RT)
Salesman whose job it is to know quotes me R 12,000 ± for supply and fit.
Based on above I go ahead and do the deal. I pay full asking price and take delivery. (DID NOT PAY THE R12,000.00 FOR THE RADIO YET)

I am told on delivery that I will have the price the next day for the iPod/Radio install. (Written Quote)
Chase the dealer for a week and today finally get given a price of R25602.46. (Delivery 7 Dec - Quote 13 Dec)
I complain bitterly and get offered a price of R 19201.84. (Even told their cost is R13K)
That is still R7200 odd more than I budgeted for!!!

I know I never got the quote in writing upfront but all emails between myself and the dealer they never dispute that fact.
Now that I want to order the system and pay my R12,000.00 as quoted upfront, it's all gone wrong.

What would you do, recommend?