I'm going to buy a 2005 Giant OCR1 within the next few weeks and I want to change it from a triple to a double (no stock double is available). It comes with a Truvativ Elita 30/42/52T Crank. I was wondering if anyone could tell me how much it should cost me (assuming I sell the parts I'm replacing) to switch to a double and which double would be a good buy.