The most common and most likely answer to this crossword clue is the 8 letter word GENTRIFY
I've seen this crossword clue in The Guardian
G
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More clues leading to the result GENTRIFY
Buddy explains!

The straight part
We know that "Renovate expensively" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case renovate expensively = gentrify.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 GENTRIFY mean?
GENTRIFY verb- To renovate or improve something, especially housing or district, to make it more appealing to the middle classes (often with the negative association of pricing out existing residents)