So, you're looking at a wireless, outdoor speaker system that uses an ipod as a source...
The question is, "Is the Soundcast the only option you'll consider?"
There's a several things making this expensive. 1) It's wireless, 2) it's weatherproof, 3) It's using a component that is specifically designed with an iPod dock. On top of that, just reading a review, it looks like this is a very nice outdoor speaker system. Top of the line as far as this niche product goes (hi-frequency 2.4-2.85Ghz band, controllable at the speaker, long 10 hour battery life, and pretty good output). Add to that, it's a new product. I don't think you'll find it for much less money anywhere.
If you want to be creative, you can probably piece together a superior system sonically for less, but it will take effort and it likely won't be so pretty. Depends on your priorities. Personally, to save a few bucks, if I wanted something beyond what a good boom-box would deliver outdoors, I'd run wires and set up real speakers.
I can't help you find this for less than the MSRP, but it won't be too long and I'm sure there will be some online retailer killing us authorized resellers income.
I have had the pleasure of listening and playing with the Outcast, and it is worth every penny. It worked very well from a functional perspective, and sounded fantastic. As the owner of a small custom integration company part of my bread and butter is outdoor speaker installs - I don't make too much money for my pocket on the speakers and amps because I have to compete with big-box store prices - but I do earn a good portion of my living on the fees charged for the labor (which I do most of myself) of running the cable and integrating with either the new or existing components. Needless to say, by referring this product it nips in to my income a little.
A decent outdoor speaker install, integrated with the indoor audio system and including "hidden wiring" easily runs in the $600-1000 range for my average customers, and in many cases the cost is much greater (due, mostly to their tastes). Granted, you can acheive decent outdoor audio for much less... the boombox, or the old living room speakers strewn out on the patio tethered to the stereo.
In the past, I would NEVER recommend wireless audio components such as the Outcast - or Soundcast's iCast even - they just didn't work that well and sounded even worse. After recently playing with both the iCast and Outcast and most of all hearing the Outcast first hand, I am a true beliver that this gem is worth every penny. I am not too big in to iPod music, but it is great for those who are since the Outcast does wireless control the iPod, and also the iCast transmitter includes an iPod dock... but don't over look that both the iCast transmitter and the Outcast speaker itself both have RCA inputs, so you are not limited to just iPod tunes.