I've spent way too much time hunting for decent interactive stuff that doesn't cost a fortune. The free scene really is scattered all over the place, and quality varies wildly. If you're okay with text-based interfaces and older designs, the Choice of Games host a lot of free-to-try demos. Some of their romance titles have pretty steamy paths you can explore for a good chunk of the story before hitting a paywall.
For purely adult-focused material, I usually end up on sites like Chyoa-dot-com. It's community-driven, so you get a wild mix of quality, but the tagging system helps you filter for your specific kinks. The stories are broken into user-submitted segments, and you click your way through. Just brace yourself for some real rough drafts and abandoned narratives mixed in with the good stuff.
My bookmark folder is a mess of forums and smaller sites. I found a couple of gems on a subreddit dedicated to interactive fiction, but you have to dig through a lot of 'my first try' posts. Honestly, half the time I just want something that doesn't crash my phone browser.