@ haines...As far as I know the skier to skier price does not require any equipment trade in.
DW gives a great description of Accuski...my ski buddy's boat has Accuski and I have SG in my MC; we swap boats everytime we ski. Comparing with SG, Accuski is a little more challenging to use...it requires crew weight, skier weight settings which can be saved, as DW describes above, as long as you remember to change the settings btwn skiers. You also have to adjust the RPM setting for each pass based on the winds that day to get accurate course times. Even though I drive this system alot, I will occasionally forget to press the foot to engage it. Also, as DW mentioned, parts are sometimes challenging to get since the system is no longer produced, but the previous company owner lives in central Florida and does his best to help you out.
Accuski does provide a good pull, but I believe SG is more accurate time wise from segment to segment in the course if I understand how both systems work. SG is definitely easier to use and requires no inputs as far crew wt, skier wt, winds, etc, just turn it on and go...perfect times every time!