The Korg Minilogue is a really good beginner synth. It has a what you see is what you get interface, and even has an an oscilliscope which relly helps starting out. Here's a video plugging this as a great beginner's synth: https://www.youtube.com/watch?v=EE7EvKYTs4I
if you look at the recently sold on reverb, you see you can get one for ~$300 or ~$350. https://reverb.com/marketplace?query=Korg%20Minilogue&show_o...