My macbook has crazy horizontal lines on the screen that get worse the longer it is opened and the screen eventually turns all white. If i hold the left side of the screen in a strategically found angle (that changes multiple times each use), the screen is fine. But really, who wants to do everything with one hand while using the other to hold the screen. Any ideas what could be wrong and how much it will cost to fix?

Yeah do it yourself for 70 bucks on ebay go to ifixit and read the guide. One more thing you may to go buy yourself a inverter cable to be on the safe side that may be your problem all together buy em both. Easy fix.

Most of the time it is either screen cable or inverter which we can do within an hour.

It will approximately cost you £75.00.