My biggest complaint about powerheads is that suction cups suck! Or that.. they fail to suck after a while. I pretty much switched all mine to magnet holders (or clip ons).
Eductors are nozzles on the pipe outputs that use a venturi/bernoulli principle to move more water, you get a fan shaped output of water movement. You need a pressure rated pump though since they put a lot of backpressure on the pump.
http://www.kthsales.com/website/vend...g_eductors.htm
I dunno I'm pretty happy with Tunzes but I agree they're costly. But the energy consumption is definitely a nice payback and they put out a nice flow. I even have one (one of the smaller models) in my FW tank.
On a tank like yours though I guess you're not looking at a huge pump, probably something like a mak4 or something like that would be adequate.
One nice thing you can do with a closed loop, I think people call them Calfo manifolds since Calfo was one who talked about this idea a lot, you create a loop of pipe that sits on the tank perimeter. Then you add as many outputs on T's down into the tank that you want. The nice thing is that this is a great way to get a customized flow pattern, while keeping the majority of the hardware out of sight.