Outdoor powerpoint shouldnt cost more than 100 bucks.
Depends if it's a brick house, where the pump is and where you can run a junction from (or where the switchboard is)
No idea why you'd need a 15 amp point for this, my davey pump which pumps up to 60L/min runs at 400 - 800 watts.
Sparkies may want to run this as a separate CB to the switchboard, but if you have a double outdoor point close (ie. for a hot water or ducted heating
system) then i'd just plug it into that - typically these only draw a wee bit of power for ignition instead of a pilot light.
Noise on the circuit? Well maybe, but many solar hot water systems have pumps as well.
I've spoken to sparkies who say you can have up to 10 power points on the one circuit.
Really just depends on the expected load you're gonna put on it.