Unless you live out in Timbuktu, I'd say your chances of finding "an excellent condition blued Python with 6" barrel" are very very good. I see them all the time at gun shows. All it takes is money!
Prices are regionally based. Higher is some areas and lower in others. To cover the whole spectrum I'd say you can easily find one in LNIB condition for between $800 and $950. If no box or paperwork or replacement grips or any non perfect finish (but still excellent overall) $700 to $800.