Because of the recent increase in fuel prices, the price of food is more expensive than before.
This is obviously a direct translation of harganya lebih mahal!
This is really a collocation problem. The IELTS examiner will understand what you mean, but you will not receive a good score for vocabulary. A product or service can be expensive, but the price of the product or service is either high or low.
More correct collocation is as follows:
Meanwhile here’s a song illustrating some common collocations when talking about money.