I usually look here when I'm trying to get a good idea for prices. I wouldn't go with anything that isn't UL listed, it is required for grid-tie and in general I don't see why someone wouldn't want listed panels. Keep in mind that there are much higher costs than the panels themselves when you factor in the total once you've got your racking, inverter(s), permitting, and if you need labor you'd want to factor that in as well. Normally(from what I read and from discussions with people who install these systems) installed costs prior to government rebates is $4+ per nominal watt if a system is professionally installed at about a 4kw size(factor in economies of scale). Not sure what the labor component is in that number though for those doing it themselves. Also, don't forget about shipping costs for all of these components, they are large and heavy.
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