"Very few metals are as costly as gold." The correct comparative form of the sentence is-

• Very few যুক্ত Positive Degree কে Comparative Degree তে রূপান্তর করার নিয়ম:
প্রদত্ত sentence এর শেষের subject + verb + positive degree এর comparative form + than most other + Very few এর পর থেকে verb এর পূর্ব পর্যন্ত।
 
→ Positive: Very few students are as good as Lablu.
→ Comparative: Lablu is better than most other students.
→ Positive: Very few insects are as busy as a bee.
→ Comparative: A bee is busier than most other insects.

Positive: Very few metals are as costly as gold.
Comparative: Gold is costlier than most other metals.
 
Source: A Passage To The English Language by S. M. Zakir Hussain.