having the carbs cleaned by a shop will vary on what they charge for labor, I would think a good shop can get them off and cleaned and back on in about 2 hrs
a lot comes down to HOW they clean them, do they allow to soak for a while in a solution, scrub clean, or use an ultra sonic cleaner?
a lot of times I would think HOW They clean them comes down to HOW dirty they are, ethanol leaves behind a varnish like coating that can be from easy to get off tot almost impossible(boiling in lemon juice helps, as a home remedy)
if your going to go with a rebuild kit on each carb, then that add's to there costs
JUST spraying with carb cleaner doesn't work really on any carb thats been sitting
Higher Octane fuel, doesn't have much benefits to your motor unless it has work done to to to need it
I have friends the refinery busines that MAKE gaoline(diesel and kero and heating oil too)
and they all tell me HIGH grade gas, gets more cleaners in it, and as such, MIGHT help running from helping clean things,
it in many area's might NOT have ethanol in it too, I know several stations by me, there high grade is ethanol free here in my area, BUT not every where!
another advantage of higher octane fuel, is, ALL fuel looses octane as time goes by, so starting off higher, leave more wiggle room say is it staying at or above the 87 needed for these older sleds!
your best bet is to call a few shops near you and ask what they would charge to clean your carbs and and set things up, synchronize all 3 , so there working all at same time to get the most out of your sled!