Looks like WWStereo is running a sale on amps. I just picked up an ST-4X II for $99 to go with my ST-4X SQ and ST-1350X. not a bad price as it goes for double that on Woofersetc and it claims to be an authorized dealer with full warranty and 60 day return policy.
Zapco ST-4X II for $99.99
Zapco ST-4XP for $149.99
Zapco ST-2X SQ for $79.95
These were a few I was watching, and it looks like they have good deals on a bunch of other stuff too. I'm not affiliated with them, but have been watching for deals on these specific amps and was happy to see this one today. I'd been watching these specific listings and they all dropped by $50ish today.