The price of natural pearls is more expensive than the price of man made pearls.

 This is an Indonesian student translating ‘harganya mahal‘!

We see what you mean. But in IELTS if you want a better score for vocabulary (LR)¹, and if you want to be more accurate with meaning (FC, TA, TR, CC)¹, then you need better collocation (LR)¹.

First of all ‘price‘ can be ‘high‘ or ‘low‘:

• The price of natural pearls is higher than the price of man made pearls.

Products and services, meanwhile, can be ‘cheap’ or ‘expensive’:

• Natural pearls are more expensive than man made pearls.

We can use the same collocation to talk about this bottle of wine:

• Penfolds Grange Hermitage 1951 is very expensive. Only a rich person can afford to pay such a high price for wine!

If you say the price is expensive, strictly speaking you are saying that a sequence of numbers (in this case $38,420) is expensive! The wine is expensive, not the numbers!

Here’s a song illustrating common collocations involving ‘price’.

(See IELTS public band descriptors)