Another "economical" solution is the Sea&Sea YS-60 kit with the Heinrichs-Weikamp adapter.
The strobe is available from Sea&Sea's clearance page for $135 and includes the strobe, a base and a handle/very simple arm. It's not the most modern strobe out there, but the power output is the same as the more modern YS-110. The YS-60 does lack many of the other features of the YS-110 though.
The H-W DA adapter will trigger it from the camera's internal flash (available for $130 from Reef Photo) and supposedly will even get the strobe to mimic preflashes. I just got the strobe kit and am still waiting for the HW adapter to arrive before trying it out, but I have been assured by various people that it will work.
All in all, under $300 for a complete setup with decent power. I figure the strobe will at least be useable as a second or fill strobe should I decide to upgrade my system in the future.
This is the setup I use with a Canon A620. I already had the strobe, so this was the cheapest way to go for me. I think you can buy the strobe pretty cheap directly from Sea & Sea in the closeout area of their website.
Although they are nothing special, you can take a look at some of my photos here: Flickr: Photos from jvdk01
Almost all the underwater photos were taken with this setup.
Good luck
John