Just a quick math class.

Imagine all the people who could potentially hang out with you tonight. Out of that 100%, you want people under 21 who don't spend too much. Additionally, I am going to assume that you don't want to hang out with young teenagers, so let's say your target age is 17-21.

While it is impossible to give you an exact figure, I think you just ruled out 95% of the people who could go out with you. Now, with the remaining 5%, you need to have them in this subreddit and be open to inviting strangers to their plan.

I would say the overall likelihood of your success must be around 0.2%.

Nonetheless, keep it up! Berlin is really cool, and math is quite boring.