Wednesday 24 June Market Maker has your money., page-83

I haven't actually checked a calc with the IG fee structure, so worth having a look.

With 1 contract ($25) the costs for 24 hours would be:

Aus200 Cash: $25 (1 tick spread) + (25 * 6000 * 2.5%/365) = $35
Aus200 Future: $75 (3 tick spread)

However the cash cost would go up by $10 each night that is held, so Futures start being cheaper after day 5 for this example.

Note: the spread is larger out of hours, something along the lines of 3 ticks for Cash, and 7 ticks for Futures.