Don't pay full price. On site, there will be folks offering substantial discounts.
GrayLine, for example, leaves from Graumann's Chinese Theatre. In stead of buying your tickets in advance, just go and see what the ticket sellers are offering. If you want one of those cheesy (but informative and beautiful) jeep tours of the 'Stars Homes' - then just see what they are offering on the street. PS, there is a lot of animosity in LA to tourists who go on these tours, so don't be surprised if you get the finger from cars passing by.