Also worth searching the internet for discount codes for the website you're thinking of getting your DA polisher from.
Waxamomo, who are sponsors of the detailing section on this forum also run periodic discount promotions. They were running a 15% discount off everything (apart from pressure washers) in early May, so worth checking the detailing section regularly for details of any current special offers.
Forum members get a regular 5% discount by using the discount code ilovewaxamomo