A good replacement R/R can cost 70-80 if you upgrade to the MOSFET kits (which I am confident they are NOT doing), otherwise $40-50 for a standard off-the-shelf replacement (they aren't that great).
Batteries are about $50-60 for AGMs when I buy them. That's $100-120 in parts, and I guess the rest they're tacking you for is labor.
1986 Kawasaki Vulcan 750
NGK Iridium Plugs #7803/DPR7EIX-9
Duralast Gold ETX15 AGM Battery
Coastered & Shaved
Metzeler ME880 [110/90-19, 170/80-15]
Balance Dampers Replaced
Rebuilt Forks w/ Progressive Springs
VN750.com Grill Cover
Emgo 23-92411 Handlebars
MOSFET FH012AA R/R
1990 Kawasaki Vulcan 750
1998 Honda VFR800 FI
2014 Honda VFR800F
1989 Pontiac Firebird Formula 350