DIGITAL:

12/12/2018 = $4,800 for Ponto 3 SuperPower with its soft and hard ($100) bands. 
             Free trial/demo, with its headband, since 11/19/2018.

6/12/2015 = $1,995 for Sumo DM BTE + $200 headband, cord, & bone 
conduction oscillator BC462 100

--

ANALOG:

380P (company said it came out in 1994):
11/29?/2011 = $1,300
11/22/2005 = $1,000
9/2/1999 = $1,000

E328P from 1989
E38P from 90s?

I probably have more somewhere else! :O