Bucks laid out, investing in gems mostly, or toy design (6,4)
I believe the answer is:
Here is my best explanation:
'toy design' is the definition.
(Rubik's cube is a toy)
'bucks laid out investing in gems mostly' is the wordplay.
'laid out' is an anagram indicator.
'investing in' is an insertion indicator.
'gems' becomes 'rubies' (ruby is a kind of gem).
'mostly' means to remove the last letter.
'bucks' is an anagram of 'kscub'.
'rubies' with its final letter taken off is 'rubie'.
'kscub' placed within 'rubie' is 'RUBIKS CUBE'.
'or' acts as a link.