Hi aharrin1,
An STEC System 20 will run about $ 8000 Equipment and 40 hours or about $ 11,400 (@ $85 per hour)
A System 30 with altitude hold will run about $ 12,500 equipment and 50 hours or about $ 16,750.
This is based on STEC/Cobham 2013 pricing.  You can add GPSS Roll Steering to either autopilot for about $2800
installed.  STEC/Cobham makes a good autopilot but they have been "price aggressive" through the last fours years when most avionics manufacturers have held the line on prices during these tough four years.  That's my only complaint
about STEC/Cobham.  Frankly, it's hard to justify an autopilot installation these days unless you plan to keep the plane for sometime or are into it "real good".  In most cases, you won't recover your investment with airplane values dropping, especially among the "legacy" Cessna and Pipers.  The alternative is to find a good autopilot mechanic who can keep that ARC 200A working.  Bob Hart  APG Eastern Avionics   www.avionix.com