Octoparse has a free tier and a Google scholar template. No idea about other sources. Ultimately Google scholar / research gate etc don’t provide their own RSS feeds so any solution you use is going to involve someone tweaking a scraping template over time to keep up with changes to the source websites. = Cost.

I used to just use email notifications instead and had a filter for these in my inbox which had the same effect as an RSS feed…

yeah it’s called abstract, it’s always free to read on publisher’s site

if you want all of article go to scihub (pre-2022 articles) some are in anna’s archive