There is no need to replace the stock shock.  The shock will have to be shortened, of course, and we'll have Gold Valve Setups for them.  The spring will need to be changed as well (shorter and stiffer).  Shortening, Gold Valve, Spring and Special Spacer including labor will be around $550-$600.  There are no "off-the-shelf" aftermarket shocks that are setup perfectly for this application anyway but this would be about a $1500 option so I don't recommend it.

On the rear we shorten, change the bottoming point, custom valve a Gold Valve, re-spring, and add a Rebound Separator Valve.  It is vitally important we setup the proper rear anti-squat in this process.  Keep in mind the shock dimensions work hand-in-hand with the front end geometry.

Move Bottom-Out Point Hardware –
Mod bottom-out bumper
Lowering Spacers
Gold Valve Kit Conversion (in house)
Rear Spring
Rebound Separator Valve
Fork Rebuild Labor
Ultra Slick Fluid
Oil and Dust Seals
SHOCK ONLY TOTAL  (plus tax)
Remove & Replace Rear Shock (complete bike)
COMPLETE BIKE TOTAL  (plus tax) with options

We also highly recommend:
Scotts Steering Damper - www.scottsperformance.com
QTM – Brakes & Marchesini Wheels - www.qtmi.com
Catilyst Body Work - www.catalystracingcomposites.com You will need to make Rear Sets and an Instrument Mount racetech.com