I've decided to put power windows into my second car, simply because of how easy it has made life in my car (no more kids kicking winder handles) and how effective and reliable it has been in my car (after 6 months of use they are still working as well as the day I installed them).
These kits can be bought for an EXCELLENT price off eBay from this store:
or straight from their online store here: http://www.rapidelectronics.com.au/
You can email them directly with enquiries here: firstname.lastname@example.org
This store also sells a lot of other interesting products such as central locking so check them out, their prices always seem to be very good.