Ok.
There is a HUGE bewildering array of keyboards available for around
$300 or less.
I am looking for something for my young kids to play on as well as for
me to try to learn piano.
I was thinking that these would be the minimum criteria

-full sized, touch-sensitive keys, preferring 76 keys over 61, if
affordable
-general MIDI
-USB connection to a Mac or a PC
-very good sound quality
-a good number of built in voices/instruments, tempos, ...
-good user interface, decent LCD, readable, ...

If I had my choice, I would choose 76 keys over 61.