Congrats.
For a $400 budget, look for a used Kenwood TS-120, 130 or 140 (or equivalents from Yaesu or Icom like an IC-720, 730, 735, 740, etc.), a 20 amp power supply, a used antenna tuner, and a multi-band dipole like a G5RV and/or a Carolina Windom antenna.
You'll be up and running on...