KHOBAR, Saudi Arabia, May 14 (Reuters) - The expansion of a petrochemicals complex in Saudi Arabia owned by Saudi Aramco and Sumitomo Chemical is **w expected to cost 32 billion riyals ($8.5 billion), higher than previously estimated, the joint-venture said on Wednesday. The expansion plan, which aims to increase output from the plant as well as introduce higher-margin products, was originally estimated to cost around $7 billion. But in a stock exchange filing on Wednesday, PetroRabigh said: \"Total investment in the project is around 32 billion riyals according to current forecasts.\" The statement did **t give any reason for the change in price, but said the project - situated on Saudi Arabia's Red Sea coast - was still due to come online during 2016. The joint-venture, k**wn as PetroRabigh, has had a number of setbacks because of maintenance issues in 2013 at its existing facility including power cuts and an outage at its ethane *****er.