It depends partly on where you are. If you're in the People's Republic of California, for example, it's worth more than the identical gun made on the same day if you're in Nebraska or Idaho or South Carolina.
I paid $800 for an eight-inch Python two years ago, and considered it reasonably priced, although it turned out to need an action job. If Pythons are common where you are, you might have to wait awhile, but ought to be able to get at least $750 for it. The six-inch models are the most common, followed by the four-inchers. I'm not sure whether there's more demand for eight-inch models or the 2.5-incher snub-nosed model, but do know the latter two are hard to find. Eight-inch Pythons are generally in pretty good condition, since they were favored by target shooters and people who take hunting very seriously; the shorties, by contrast, have usually been carried in holsters and pockets, and show more wear.
If I were selling your Python in Colorado, I'd ask $1,200, and let a serious buyer haggle me down to $1,000, but only if he promised to give it a good home and treat it with T.L.C. If I were considering buying it, I'd offer $700 or $750, and let myself be haggled up to $850 for a really minty Python with a superior action. If you're in a state where such guns can't be so-called "imported," add $100 to $250 to the price.
All that saidâ„¢, I'll be the first to admit Pythons are ludicrously overpriced.