cheapest of all

Vincent TeoCan I Say,

(a) The durian is the cheapest of all.

I'd write: This is the cheapest durian instead of writing a long-winded sentence. (I've changed 'The' to 'This'.)

It depends on what you mean. What is a durian? Is is the cheapest of several alternatives you've been considering?

I'm looking at cars. I've looked at a Land Rover, a Mercedes, a Covette, and a Kia. The Kia is the cheapest of them.

I just want to ask, is there correct to say ".... of all"?

I think you can:

Cambridge Shopping Guide to Organic and Health Food

This place is definitely the cheapest of all, but the choice is limited. Big variety of nuts, dry fruit, flakes and everything which lasts longer. .

Vincent TeoI just want to ask, is there correct to say ".... of all"?

I agree with Marius that you can say "... cheapest of all". However, IMO, you should change "The" to "This" or "That". Therefore, you can say "This/That durian is the cheapest of all" (meaing it is the cheapest compared with the other durians). But it is better if the sentence is rephra