Another vote for the 2 or 3 way "super 12s", especially the fEARful 12/6 cabs.
Weigh around 40 lbs (often less).
Can easily handle anything a 450 watt amp can throw at them.
And...
If you're handy with a saw, you can build them youself and save some $$$$.
I'm no expert, but I think the fEarful cabs are all designed to have a flat frequency curve. The 15" cabs go a few dB louder but should technically have the same sound as a 12" fEarful.
You might check out Genz Benz cabs as well. You could stack two 12t shuttle cabs and fit them easily in a Focus.