Odds of a race finish paying out (8)

I believe the answer is:
spending
'paying out' is the definition.
'spending' can be an answer for 'paying' (spending is a kind of paying). I'm not certain of the 'out' bit.
'odds of a race finish' is the wordplay.
'odds of a race' becomes 'sp' (I can't explain this - if you can you should give a lot more credence to this answer).
'finish' becomes 'ending' (I've seen this before).
'sp'+'ending'='SPENDING'
Can you help me to learn more?
(Other definitions for spending that I've seen before include "expenses" , "'''Getting and ..., we lay waste our powers'' (Wordsworth) (8)'" , "Using money or passing time" , "Laying out time or money" , "splashing out?" .)
