4Q Sunrun(now merged with Vivint) numbers are out. If you want an answer to the original question, their sales cost is noted as $.85/Watt for 4Q20 and likely doesn't include a LOT of indirect sales cost that's baked into general costs.
So Tesla is selling installs at $2.01/Watt and the #1 installer in the nation by far likely has a cost line >50% of that for just sales.
I'm still amazed at how many people are unaware of solar as a reasonable alternative to whatever their status quo is. I've got neighbors who just think Solar is a luxury that doesn't have much short or long term value.
Sunrun spends an outrageous amount on lead-gen, affiliates, inside sales, and other functions. Tesla just assumes interested leads who do basic research on Google will stumble upon their offering with little fuss.
It'll be interesting to see how the race to the bottom pricing affects the industry in the long-term.