How much would you need to pay per year to have an ad-free twitter?

I use twitter, and I have done since something like 2006. I'm a white guy, with a follower count in the mid two thousands, so as a result, the biggest problem I get from the site is keeping up with all the tabs I end up opening from it, rather than abuse like other folks I know.

Every now and again, I see a tweet like this (link to tweet):

I have a revolutionary idea. Hear me out: How about if we *pay* a small subscription fee for Twitter and they stop fucking everything up trying to make money every way except charging for their service.

There was another example, by Ben Hammersley saying largely the same thing last year, but since he started deleting his tweets automatically, I can't point to it now.

Anyway the gist is the same - why don't we just club together to buy it out? If we did that it wouldn't be the same cesspit is now, compared to the fun service is was when we started?

I like the idea for this, but I think it would cost more than most people are prepared to pay - something in the region of 200 - 250 USD is my best guess, to make more money than Twitter's own reporting said it makes from advertising.

Given that app.net and others weren't able to charge anywhere near that and fizzled out, I'm not sure how this would end up better for Twitter.

My workings

My workings and assumptions are in this spreadsheet, which I shared last time I saw this idea, and I'd really be interested in hearing which assumptions ought to be updated to make this possible, as I've shared mine below:

https://docs.google.com/spreadsheets/d/1Baa08XSFCL1O8dvlMit8fnEjaGjxfZNrtVR9GDWh1lE/edit#gid=0

Make a copy, share a link back.

If that's not your jam, the comments are open below, and my DMs are open on twitter - I'm @mrchrisadams.