Quando vou plotar os dados com a biblioteca Matplotlib e executo o bloco de comandos:

import matplotlib.pyplot as plt
plt.contourf(xx, yy, Z, alpha=0.3)
plt.scatter(teste_x.horas_esperadas, teste_x.preco, c=teste_y, s=1)

Recebo esta saída:

TypeError                                 Traceback (most recent call last)
<ipython-input-15-5e679b570130> in <module>()
      1 import matplotlib.pyplot as plt
----> 2 plt.contourf(xx, yy, Z, alpha=0.3)
      3 plt.scatter(teste_x.horas_esperadas, teste_x.preco, c=teste_y, s=1)

6 frames
/usr/local/lib/python3.7/dist-packages/matplotlib/contour.py in _check_xyz(self, args, kwargs)
   1506 
   1507         if z.ndim != 2:
-> 1508             raise TypeError(f"Input z must be 2D, not {z.ndim}D")
   1509         if z.shape[0] < 2 or z.shape[1] < 2:
   1510             raise TypeError(f"Input z must be at least a (2, 2) shaped array, "

TypeError: Input z must be 2D, not 1D