Are there crowdsourced feedback platforms, or does somebody know where I can find somebody that does not ask a lot of money for checking some research articles that I have written for mistakes in grammar, spelling, punctuation etc so that I can deliver this file as a pdf or tex and have it commented on or corrected. (I know there are organisations that can do this but this is a little bit expensive)
If your only requirements are to check mistakes in grammar, spelling and punctuation, then you can use grammar checking tools(or websites) such as https://www.grammarly.com I have used it personally and it's easy and efficient to use and free of cost.
But, if you want other people to give feedback on your content, https://www.kalaage.net can be a helpful website for you. Proofreading of your content will be done by the users at this website(who will get paid by the website itself for this task)
P.S. This is not an advertisement. I don't work for these sites. I have personally used the first website but I don't know much about the second site. I just mentioned because its one of the sites which can be used for crowdsourced proofreading (I can't guarantee you for the quality of proofreading)