How to pursuade my mother into buying me a Honda Cr-Z?

My mother said she will purchase me a vehicle as long as it is in the price range of what my sister's car was. In 2008 we bought my sister a honda civic 2008 and it was around 19k. During that time of the year, I was doing a project in my business and marketing class and was searching up hybrid cars. And I saw the prototype of the Cr-Z in Japan and from that day, I fell in love with it. I wanted it too bad. So when it came out this year, I had to get it. The price range for the Cr-Z, not the Cr-Z EX is around 19-21k. That's around my sister's price range but the thing is, she doesn't want me to have a two seater . So how can I convince my mother to buy this car for me? ): I've been wanting this car for too long to have the chance pass up just because it's a two seater. T____T