I'm not in the business, nor am I an expert. Simply a guesstimate:
IMHO, Pythons in general are overpriced. Last I looked, a blue 4" shooter went for between $1200 & $1500 ($1500+ is just stupid for shooters, IMHO), depending on circumstance, condition & so forth.
I'd think somewhere between $800 to $1000 would be a reasonable range, depending on the usual (local market, desperation, etc.) factors.