Average price for side skirts for Lancers should be around $300 - painted and installed.

Some shops I know of:
The Spoiler Shop - Myaree (As evoposer mentioned)
Spoilers 'n' Flares - Bayswater
Spoiler Factory - Armadale
Car Quest - East Perth
Fibre Vision - Cannington

There are a few others.
Also, do a search on websites (mainly from over east) that can ship over kits specific for your car.
eg: www.ssv.com.au

Here's another option for your boot spoiler:
Explore some wreckers. You might find one cheap cheap.
Is there a reason why you're going for the Mitsu brand one?
imo $550 is too much to pay for something that (as said before) every 2nd Lancer has.

 

I dunno, I just like the look of the Mistu spoiler as it isn't over the top and makes the car look good even if you don't have any other part of the body done up. It also makes the car look smooth and the spoiler naturally looks like a proper part of the car (unlike the spoilers on those Pulsar Plus's, how ugly and artificial do those look!). But because the general concensus here from you guys (who are more knowledgeble than me) is that $550 is a rip off, I will certainly look into other types of spoilers instead.

Do these spoiler shops usually have pictures of spoilers to show what they look like on a Lancer? My personal preference are spoilers that look similar to the Mitsu one, although maybe slightly lower (I've seen some of those around on slightly older Lancers, I think from 1997/98, although I can't say for certain what year it is).

 

yeah the places have plenty of pics....................
keep it simple then if u like it like that.

 

Keep you eye out and look in the trading post and other places people advertise parts. I often see the standard spoilers off Lancers in there. Most of the time they will be hardly used because they have done a full kit. They are quite cheap around $200 and all you have to do is paint and fit, which is even easy enough to do yourself