Getting back to the home electric organ of the OP, I’m surprized that nobody has mentioned the number song books yet (well, maybe there’s a good reason, or maybe somebody has). My mother had a basic home electric organ (actually still does - it’s been in the hall for at least a decade or more, unplayed and serving to support several potted house plants for that long) - when she used to play, she would use song books w/ numbers corresponding to the keys (she could not read music in the normal fashion), such song books being readily available during the '70s & '80s at fine stores such as Woolworths & Newberry’s (and maybe even Alexanders!). She wasn’t particularly good (to be fair, the few times I tried it, neither was I), but she liked it and was quite happy when she played a song smoothly with no missed notes. Of course, the songs were not really what I wanted to hear (since the books did not have any songs by The Who, Boston, Zep or Pink Floyd, and only the most mellow songs of the Beatles), but I was slightly surprized to find the theme from MAS*H (Suicide is Painless) in one of the books (with Lyrics - Hey Mom! This ain’t no happy, peppy song!)
Concurring with what 1920s Style “Death Ray” said: My Roland 88 key “electric piano” (not keyboard - or at least, that’s not how they advertise them - see my description above of included features) had a list price of $1K in 2001 - the kind friend who bought mine got a significant discount - he’s an expert shopper. I knew what he paid only because the shipping list had the price on it, otherwise, I wouldn’t. I think he’d have been unhappy if he’d known.
I’d expect them to be cheaper today, given how much cheaper the various transistors, etc., have gotten in the last few years. Of course, unless you want to listen on headphones, you have to spring for speakers, but they take regular stereo speakers (NOT computer speakers - the output from those sounds horrible!). You can, of course, get one with built in speakers, but I’d be quite skeptical about the quality of built-in speakers. I’d want to “audition” it, extensively. 
There are several brand names that produce electric pianos of very high quality, the next best thing to a real, acoustic piano.
And there are always such things listed on eBay at lower prices. Sometimes the savings can be substantial. The only cautions I’d make would be
- be sure of the feedback rating of the seller
- the seller is the owner, not one of those businesses that list for other people.
I rarely even consider an eBay seller with a rating of less than 99% - and now that eBay has started only using the current year’s FB to calculate the official number, I am even more careful than in the past to scan over at least a few hundred FBs. When you switch the pages to 200 per page, it doesn’t take long to look through 3-5 pages, just scanning for the red dots. Many times, a negative is really unearned - FB from a newbie who doesn’t understand what proper grounds are for a negative. That may be why they stopped using older FB, but they also made it impossible for sellers to reciprocate, which I think is wrong, even though I’ve bought lots more than I’ve sold. Sellers need reasonable recourse. But I think twice (or more) about people with poor ratings, and also about newbie sellers.
Yes. Mine has built in speakers. They are adequate but it sounds a lot better through headphones. If ever I decide that I need the speakers to sound better I’ll buy some external ones. I actually didn’t audition my keyboard at all as no one has any within 1000 miles of my home. I managed to audition a few different models that had the same specific type of weighted keys so I could get an idea of the feel, but I took the sound on faith (and internet reviews.)
Edit: I’m very happy with the sound of it through headphones which is how I normally use it, and one of its great advantages over an acoustic piano.