kiwis

Yea sounds about right - I was getting it from Countdown and from memory it was around $6-7

Think dilution.  The more diluted the ammonia is the safer for the fish. A small amount of ammonia in the water (below 1ppm) won't harm the fish and the bacteria population in the filter will eventually grow enough to deal with this amount.  When this happens another fish can be added to increase the amount of waste etc, the ammonia levels rise again then time is needed for the bacteria population growth to catch up to this level and so on.    
Advantage:  you get to have life in your tank straight away.
Disadvantage: You have to keep a constant eye on the ammonia then nitrite levels (the fishes life is at stake) and it takes longer to get a fully stocked tank.
With a fishless cycle you can get the ammonia level up to 4ppm so more food for the bacteria = faster bacteria population growth = faster cycle = fully stocked tank sooner. 
I won't say " a couple of small clowns in a 140L is Ok" because it all depends on whats considered small and how fast the bacteria population grows (depends on filter system, water parameters) etc.  Every tank & situation is different. Instead if you go this route then test 2x a day and if the ammonia then the nitrite levels get near 1ppm do a water change.  Keep doing this until the tank is fully stocked. This is why the fishless cycle is more forgiving and safer for a beginner.   Throwing a couple of fish in a tank, waiting a few weeks then throwing in the rest may work out Ok for you, but there is a good chance it won't.
 

You also should probably have a small powerhead or two in the main tank for circulation in addition to the return pump.