I've been on a petsite where if you wanted to reach forum post milestones, there was a spam forum you could use as a "trash bin" to just post nonsense. It came with one downside - you had to pay in their currency per post. 50 spam posts could cost you quite a lot.

Is there a similar thing here on Subeta?

yup! there's a chit chat forum that can drive up post count to get into places like the blue building, hope this helps!

on top of the chit chat forum, another quick way to up your post count is to use the games board topics to post the winnings from various dailies. if you're doing them anyway it's nice and easy.

To answer your question: yes, there's a chit-chat/user game forum for this but it's advised against just straight up spamming (there's a difference between spam and just posting to participate in the games or topics on here. I'm sure you can figure that out by looking so I won't explain that.)

There isn't a cost to posting on anything on here that I'm aware of. Unless you do a billboard promoting something, that's different.