The Casio CTK-1100 is an inexpensive 5 octave keyboard, suitable for beginners.
It has a few limitations - it isn't General MIDI (not very important unless you are working with MIDI equipment for recording etc.). It is only 12 note polyphonic - it doesn't have a huge capability if playing with all 10 fingers and using backing rhythms or chords. It isn't touch sensitive, which again isn't very important at  the first stages of learning - only later.
61 piano-type keys
Maximum Polyphony 12
Tones 100 built-in tones
Rhythms/Patterns 100 built-in rhythms
Auto Accompaniment
Modes: CASIO Chord, Fingered
Controllers: Start/Stop, Synchro/Fill-in
Built-in Songs 100 (Song Bank)
Lesson Function
Part on/off (Lesson part: right hand/left hand)
Other Functions
Song bank controller
Key Transpose 12 steps (-6 to +5 semitones)
Tuning Control A4 = approximatery 440 Hz ± 50 cents
Display ScreenLCD
Speakers 10cm x 2
Amp Output 2W?2W
Input/Output Terminals
Headphones/output (standard stereo jack)
External power (9.5V DC)
Power Requirements
Batteries: D-size x 6/Optional AC adaptor: AD-E95100L
Dimensions (W x D x H) 949 x 304 x 93mm
* Excluding music stand, and other projections
Weight
3.3kg (Excluding batteries)
Included Accessories
Song book, music stand

Qty.

    Model: 4aCA1100