Wow, what a great project. I'm an engineering undergrad, so I get a kick out of these things, too. As far as your questions go...

The size of the device, for a person or family, should be large enought to get about a dozen twelve oz drinks from it per use. That way, even for a decent sized family, you wouldnt have to be using it all the time ( And I was surprised to find that 144oz = 4259mL = 0.15ft^3 = roughly 6.5in x 6.5in x 6.5in, that seems pretty small for just the water containment. And yea, I should just be using metric, but I visualize amounts much better in my native unit system.)

I'd be easily willing to pay $100-$150 for something that could purify water without electricty at the above amount. Above that would be getting a little iffy.

If the device lasted through 2-3 hurricane seasons I'd be very pleased with the lifespan.

As far as effort goes, too much effort is when you you need the purified water to rehydrate you from the work you did to get the water safe. I would have no problem as long as I wasent sweating and tired afterwards. I'd be willing to wait if it was pretty easy, but going quickly without exerting too much energy would be nice.

If this device worked well Im sure people would use it for almost all thier water unless they had other alternatives. For ex, I would probably drink my bottled water first, but I wouldnt use that bottled water to cook with, clean or water animals/plants, I'd use the purified water.

In all, it seems like a great idea. I wish you the best in the design process and hope you come up with one that works well.