"That said, I think the big manufacturers have really missed an opportunity in exactly the opposite direction of that you suggest - I don't give a damn about efficiency or how much space it takes up, I care about price per watt."
Which is all they concentrate on. Panel prices from the factory gate have fallen from $2 to 50 cents/W in the last four years. Efficiency has crept up from 14 to maybe 16 to 17%. They are doing precisely what you ask, and you're complaining?
"Sell me 10-20KW of 5% efficient panels for 25 cents per watt, and you'd have a very happy customer."
You are forgetting that panels aren't the only things in the system. If you care to run the numbers, I think you'll find that you're almost certainly wrong.
For instance, let's say you have enough room for 8 panels, like my new garage.. To be *able* to install the panels, I'll need to run DC wire from the roof to a point near the 240V pony panel (assuming you have one, if not...), put an inverter at that point, add a 30A breaker to the panel and connect the inverter to it, get a building permit, and then put the racking on the roof.
Racking is normally about 25 cents a watt, when measured against a typical 250 watt panel. So for a 2kW system we might expect to pay $500 for that kit. Inverters scale downward very poorly - a 2500W inverter is around 60 cents/W, while a 5000W one is around 40 cents/watt. That's because most of the parts are the same (the case, displays, controller, wiring, etc). An SMA 2500 is about $1500, while a 5k is 2200. The cabling and wiring needs to be done by an electrician and might take 1/2 a day, so let's say $750. The building permit, if you need engineering, is about $750 total. Total install time is about 2 man-days, so let's add $500 flat. Ok with that?
OK, so using 250W panels at 80 cents:
8 x 250 x 80 = $1600
+ $1500 for inverter
+ $500 for racking
+ $750 for permitting etc
+ $750 for wiring
+ $750 for install
= $5400
So that's $2.70 a watt. Ok, now let's do the same with your cheap panel:
8 x 75 x 25 = $150
+ $1500 for inverter
+ $500 for racking
+ $750 for permitting etc
+ $750 for wiring
+ $750 for install
= $2950
But now you only have 600W, so that's $6.60 a Watt. What a deal!
Yes, you can save some on the inverter, yes, you can DIY it and get rid of X and Y and Z. But I absolutely 100% assure you, the numbers end up in the same place every time, for small installs, higher wattage panels are almost *always* the way to go. If you don't believe me DO THE MATH YOURSELF.