Even the cheapest midi keyboards are velocity-sensitive. Weighting is nice, but the choice isn’t between button-presses and expression.

Are there any small keyboards that are good for playing? I'm afraid that taking out a 74-key device will be enough of a nuisance every time that it would discourage me from keeping on learning. How about a 40-key keyboard that's fine for fingers?

Pianos consume some amount of space. That's just a matter of fact with the instrument. A good digital piano in the $600-800 range with proper weighted keys will probably use the same amount of space as a dresser along some wall.

If you seriously want to learn and play piano, even as a hobby, that is the entry level.

I also disagree with using any of the popular apps as anything more than supplemental tools, but there are some very good adult lesson books can definitely form the backbone of your learning. As long as you're aware that posture and technique is a struggle for self-taught pianists, you can look for videos and make some conscious effort to improve at it.

Buying an $80 smaller midi keyboard is a good way to get a cursory feel for things without spending the full amount.

A 49-key will cover 90+% of what you’d want to do in the first year or two of traditional training. A 25-key will get annoying sooner, but if you know space is going to be a real issue, it’s just a percentage question again. You could just decide your skill will be “25-key keyboard” and adapt the training material. But I’d personally consider 49 the realistic minimum to not regularly feel claustrophobic.

There's a place for BASIC and LOGO turtles and Python, and also for $35 32-key button-smashers.

And then it turns out that Python is actually quite a useful language, and that the keyboard-shaped thing is better than nothing.

$100 vs $1000+ is a big deal.

Casio makes some tremendous keyboards these days. The Privia line is across the board excellent and can be found used for $250 or less.

Adding my vote for never ever touching an “el cheapo” instrument. A junk keyboard and guitar made me think I disliked those instruments as a younger person, and it makes me sad when I see kids struggling with instruments that I can’t make sound good with years of experience.

Digital pianos around the $500 mark are pretty good these days.

Seconded, Yamaha, Kawai and Roland all make gear in that price range that is nothing short of incredible in terms of quality and sound. Besides the fact that they don't need tuning like an acoustic would and which tends to add up over time.

Just putting in a vote for my Casio Privia PX-S1000.

Ah yes, they are also pretty good, I tried one at a music store here in nl but forgot about it. Definitely worth a mention.

Very few people can afford to blow $500 on something they don't know if they'll commit on or not.

Get secondhand for $100-150.

If you've got the space, you'll find that you can get a real upright for free in most cities in the world. Sure, it won't be the best instrument ever, but if you ask around you'll find someone chucking one out.

After a few tunings, you might wish you bought the keyboard.

Yes. We were told that we should move our piano away from the outside wall next to a window because the temperature and moisture fluctuations were causing it to go out of tune.

We're in an old house and there isn't a piano-sized space in our living room that doesn't have a window, door, or HVAC intake/vent.

That's a very important point, tunings will rapidly exceed the value of any 'cheap' piano. And typically the cheaper they are the worse they will keep tune, though there are exceptions to that rule.

I can recommend Entropy Tuner, which is a great piece of software to help you tune a piano properly.