I think $10k/yr is fairly reasonable even for startups. However, a lot of these trolls go after small businesses, don’t they?

That's the key to it all - you have HR startups, insurance firms, cybersecurity firms etc. bundle the cost of patent troll insurance into their product, give them a commission, and have them sell it to small businesses - not just startups. Then you can keep the price much more affordable because you have an economy of scale!

Excellent idea! That makes the potential market huge.

I mean kind of. They have to go for people that have money to pay them off, but not enough to make fighting them worth it. Startup is kind of nebulous, but there is a difference between a 40+ million series B startup and a small business that would balk at $10k a year. I would guess the trolls go for more of the former than the latter.

You could do different levels of protection. Have a smaller tier for smaller companies (less than a million revenue a year) for maybe 500 or 1000 a year, then larger companies pay a more. If you get one of these lawsuits, do what cloud flare have "I'm under attack" style join.