Your cheapest, best option is the Yongnuo ST-E2. About half the price of the Canon, but offers several improvements: 1) longer range; 2) swivel mount so you can point it at the Speedlites; 3) works through the camera menu system; 4) recognizes three firing groups AB&C; 5) Uses double AA batteries.
Downside is it does tend to overheat if you are doing an intensive shoot. Requiring a break in the shooting.
That is, of course, an infrared solution, so it works with the 430 and any additional 430s or 580s you might get, without any additional cost. But, it isn't a radio solution.
Due to the overheating issue, I just bought two sets of the Yongnuo 622-Cs. I've only tested them out and haven't used them yet for any real shooting, but so far, they work great. A little more expensive, but they have the advantage of being a radio system instead of Infrared. I'll keep the ST-E2 as a backup or when I don't have enough receivers. (Since you can pretty much fire an infinite number of speedlites with the ST-E2 so long as they can see the signal). By the way, I've never had any problem with the ST-E2 signal not firing a strobe, but I don't use them for long distances (although I have used them outdoors).
