I used to get paid 500€ a month as a developer for a consulting firm, and it was a 12-hours-a-day kind of a job. The firm would then bill its clients 40-60$ for every hour I worked. From one perspective it does seem exploitative. But on the other hand, I know many people who still dream of getting that job - the money is not good, but it almost doubles when you get promoted, and the career path is good. It's a really intense place with almost impossible deadlines, and you get to learn a lot from the pressure.
I was recently offered a project where I had take a complex analytics algorithm implemented in Excel to the server and implement it as an API for ~250-300$. Took me around ~20-30 hours over an extended weekend to write it in golang and I feel good about it. The work was mostly simple transformations on the input data, though a large number of them. It resulted in roughly 1000 lines of code including tests and comments, and a big part of that time was spent actually understanding the algorithm.
Similarly, I did some work as a favor to a friend - a Facebook app that would send some inspiring quotes as notifications to it's users every few days. It took me maybe 10-20 hours to get it online. Frankly, I am not so proud of the code as it was written in such a hurry, and is a bit messed up. But to its merit, it's been functional for several months without any noticeable downtime, and has sent thousands of notifications so far without any need to touch the server.
These are the kinds of projects that can be done in a short amount of time without a long-term commitment, and make sense for such a budget. For me atleast, 10$ an hour is good money, and 25$ would be pretty decent. 50$ would be something of a dream - I would be making in a day what I used to make in a month at my previous job.