Here are some sequencers you could look at (that I've personally owned)
Zaquencer - $200. The most sequencer you can get at that price point. But lots of knob turning, no real displays. Its fun though.
Toraiz Squid - $600. But it has some great features, and its very 'playable'. You can also drag and drop all of your midi from the device into the DAW.
I would suggest starting with purchasing a MIDI interface and a sequencer. Just use them to control software instruments in your DAW.
This is my workflow. Make a bunch of patterns in a sequencer. Record audio or MIDI into the DAW. Arrange the patterns. You get you brainstorming done on the hardware but the editing on the software.