There is one means of generating AI images that requires no subscription, and also lets those fascinated by parameter tweaking to access a lot more of the variables involved rather than some "safe" presets (that ensure subscriptions keep coming in) that I daresay the commercial offerings have.
This is the "AI horde" an open source distributed network of volunteers who run machines with GPUs that take in image request jobs from anyone anywhere for free, then return the result, using web based front end. No subscription required.
More info here:
https://stablehorde.net/Web interface here:
https://tinybots.net/artbot/ Make of it what you will, have a play if you want, with no investment other than time.
Full disclosure: I occasionally run a worker node and, as far as I can tell, it mostly (by a huge margin) gets used to make pics of anime, or furry, characters with unfeasibly large sexual characteristics, which is kinda disappointing, but not surprising I suppose.
All I can add regarding the whole subject, is that it's not as easy as you'd think to get anything decent out of the system. There is an art to describing things properly to realise a vision of an image that you might have. It's a fun "surprising image machine" though, if you just feed in nonsense or surreal descriptions.
I wouldn't pay for the service or be able to make a profit if I did, judging by my efforts so far!
But it has allowed me, one who can't draw or sculpt, but has the urge to create, to make some cracking custom xmas cards for my friends this year.
The tendency to a lack of conformation to physical reality in the images ( because the system knows nothing about composition, or the world ) and general weird distortion of perspective that usually turns up really does lend itself to psychedelic imagery though!
P.S. if anyone likes those "happy creature made of eyeballs, smoking" images above, they could do worse than having a look at the work of Pete Loveday:
http://bigtripcomics.com/shop.php buy some of his stuff if you want, the comix are great fun and he's clearly no stranger to the 'shroom