Basically, the difference in pricing is manufacturing costs and materials.
X Force is made in China, as are Ultrex, (out of the same Chinese manufacturer I believe), The stainless steel used is a thin walled, higher "grade" stainless than proper exhaust grade stainless. It polishes up nice, looks pretty, but when you compare the actual quality in the build and the attention to how the pipes merge, you will see the difference.
Australian made extractors are designed and manufactured here using a test vehicle. Most manufacturers will even flow test and dyno their extractors to produce optimum results.
Imported extractors are generally a copy of an existing extractor that has had small changes to the design so as not to infringe on the original maker. You can't reinvent the wheel, it already exists, but you can make it look different.
The biggest issue with imported extractors is the way they made in regards to flow. Pipe length, collector design, flange thickness etc, they all add to how the extractors perform. X Force (I am only using this brand as an example as I have removed enough of them and replaced with Pacemaker or Hurricane) have a collector that basically rams all the gases into one pipe rather than merging them. The collector is basically a 4" pipe that is formed to fit over the primary pipes and then welded. Pacemaker and Hurricane use a merge style collector that reduces slightly in diameter and directs the individual flows from the primaries into the collector. They also have an "arrow point" at the merge of the 4 pipes to aid flow. This extends the point at which the 4 pipes end and doesn't leave a void for a low pressure area to exist that will affect flow.
China has lower manufacturing costs so what ever comes out of there will be cheaper than an Australian product. Simple economics. The difference between outsourcing manufacturing and just plain copying is the standard that is applied to the product. A lot of products are developed here but are manufactured in Asia to strict standards, these are mostly good quality products, extractors are not made this way. Chinese extractors (or exhausts for that matter) are made from a sample that an Australian company has sent over just to be able to put a cheaper product on the market without going through all the R&D themselves.
Also, just to clarify, I sell a quality Australian product at a discounted price because I deal direct with the manufacturer and have no overheads. I don't sell cheap products, I just sell good products cheap.
Disclaimer: In no way am I bagging Chinese products, merely pointing out the differences between local and imported products.