When you do "thread boost", look for the "similar threads" option. Just a nickel per thread per month. And the algorithm searches all of your thread and all of the threads at all of permies to find the best matches. So your thread will appear in the "similar threads" section for up to 2000 threads. There are currently more than 500,000 threads at permies.
If you have an event, and you need to sell those tickets RIGHT NOW, then I think we have no tool that is more powerful than "similar threads". I will do a thread boost for 1000 similar threads and that will usually lead to 20,000 new views on that thread.
1000 similar threads for one month is $50.
And the similar threads stuff uses the first image in a thread as a thumbnail.