The most common and most likely answer to this crossword clue is the 12 letter word UNAFFORDABLE
I've seen this crossword clue in The Sunday Telegraph
U
N
A
F
F
O
R
D
A
B
L
E
Buddy explains!
The straight part
We know that "too steep" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case too steep = unaffordable.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does UNAFFORDABLE mean?
UNAFFORDABLE adjective- Too expensive to be afforded.