Rich, "Trading" for a home is always problematic. You trying to find a home YOU wish to own from someone who happens to also want YOUR home! Can you say "needle in a haystack!". This is often asked by someone who either A.) thinks they won't have to pay a commission or only have to pay it ONCE! B.)someone who has inflated the value of their homes.
Why don't you stick it on Craigs List IN SAN CARLOS and see if you get a nibble. Can't hurt but don't PLAN on it happening. Also, if the $850,000 is YOUR estimate then you'd best get ahold of a few Realtors and get THEIR take on the market. We've made a startling discovery with many a Seller nowadays--they think EVERYONE'S home has gone down in value except THEIRS!! Shocking!
However, the good news is you could be in an area of Sonoma (I assume your talking the CITY of rather than generic County) which have not taken the major hit of Santa Rosa or the "101" cities (exclusing Healdsburg). I hear of a Kinnybrook home in Kenwood which took a major hit in price so the market might be creeping into the more stable and/or high end areas. Good Luck!!