How do I Modify a Modified Noun

I want to say "A convenient 'cheap car'". But not, "A convenient and cheap car".

So, it`s not べんりでやすいくるま.

Can I just say べんりな「やすいくるま」, to indicate that it is a convenient "cheap car".

Another example is if I want to say "sarcastically", "That`s a spicy 'sweet food '" with the meaning of "That`s so spicy for a sweet food".

Can I just say からい　あまいたべもの? (Sounds very wrong)

EDIT:

Not limited to い・な Adjectives, how about an expensive Japanese book?
Japanese book is 日本語の本.
Expensive book is 高い本.

So, does it become 高い日本語の本?