Keep in mind that the $120 was about six years ago. Six years of additional regulation and new laws have likely bumped that to $250 per side these days.
I got a guy to scrape off the old sealent on the roof to wall joints on my motorhome roof. He wants $80/hr. He is $40/hr cheaper than the RV dealer. Auto repair shops are charging $150/hr and higher end places over $200.
So $120 seems a touch low if I hope to have it done local.
Engine Test Stand Playlist: https://www.youtube.com/playlist?list=PLwoxyUwptUcdqEb-o2ArqyiUaHW0G_C88 restoring my 1968 Firebird 400 HO convertible (Firedawg) 1965 Pontiac Catalina Safari Wagon 389 TriPower (Catwagon) 1999 JD AWS LX Lawn tractor 17hp (my daily driver) 2006 Sequoia 2017 Murano (wife's car) 202? Electric car 203? 68 Firebird /w electric engine 2007 Bayliner 175 runabout /w 3.0L Mercuiser__________________________________________________________
He is $40/hr cheaper than the RV dealer. 
Auto repair shops are charging $150/hr and higher end places over $200.
