One is a 36 cell 18v(lower under load or MPPT) panel designed for connection to a battery(via a solar charge controller) and another is a 60-cell panel with a higher voltage designed for operation in a string with an inverter. I've seen systems in Home Power magazine not too long ago designed to interface batteries with higher voltage panels but usually the charge controllers are more expensive, so there's a trade-off. If one or a few 100 watt 12v panels do the job in parallel, that's probably the best way to go but 36 cell panels are a lower volume product and generally cost more per watt.
IMHO, I consider $1.20 per watt shipped to be a great deal. My 280 watt SolarWorld Plus modules(60 cell) were just over $1/watt dropped off at my house by a local distributer but I don't think that distributor sells to non-installers and if they do, it's not at that price. I'd have to ask them though, I haven't. They were priced at a bit of a premium because they were the highest wattage units available and were picked from units giving the highest flash test result while others were producing 270 or 275. Less than one year later they now sell 300 watt 60-cell modules.
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