Adorama has the Korg Nu:Tekt NTS-1 synthesizer on sale for $78.99. MSRP is $120. The price has been fairly low on Amazon from third-parties as well, but Adorama is a Korg authorized retailer.
This is a great entry-level monophonic digital synthesizer that includes mod, delay, and reverb effects. It also allows for user-created oscillators and effects, using the same system as the Minilogue XD and Prologue. It takes audio in, so you can use it as an effects pedal for other instruments. It has a midi trs input (but does not include an adapter cable), which I recommend using as the ribbon keyboard is garbage.
Edit: Shipping is free at $80 with a filler item. Thanks to MaroonFeather262 in the comments for suggestions.