The price is NOT expensive
Because of the recent increase in fuel prices, the price of food is more expensive than before.
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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:
Because of the recent increase in fuel prices, the price of food is higher than before.
Because of the recent increase in fuel prices, food is more expensive than before.
Hope that helps!