While that kills a small piece of my soul as I’m one of those developers, I applaud people for trying to enhance their own site without spending too much.
You get what you pay for!
There’s a number of sources to get plugins online, primarily the WordPress plugins directory.
The problem here is that those plugins aren’t vetted by anyone for security, ease of use, how frequently they’re updated, what access they give the builder to your site, etc.
I often equate the plugin directory to the app store on your phone. For every one good thing, there are 1000 not good things there. Whether that’s apps or plugins, it stands true.
So where are the better plugins?
My personal go-to is CodeCanyon.
Where else should I look?
Your best bet to find a plugin that does exactly what you want is to use Google and be specific on what functionality you’re looking for.
Instead of “wordpress plugin photos”, try “wordpress plugin photo galleries with slideshow” to get more refined search results.
The more specific you are, the more likely you’ll find what you’re looking for.