See here for my estimates on the value of a gold dragon. 

As for whether it’s a realistic pot, it’s a bit tricky, because medieval tourneys don’t seem to have given out prizes in cash, but instead gave out prizes in jewelry, plate (hence why so many modern sports tournaments have “cups” as trophies), and the like. And without these objects to hand, it’s a bit hard to value how much a “gold vulture” or a “very rich ring” should be valued at, or (given how popular diamonds were in medieval tourneys) how to appraise precious stones in the abstract. 

However, I can say that 10,000 dragons work out to something on the order of 6,000-7,000 English pounds (in 1300 CE pounds, that is), which is far, far bigger than any tourney prize I can find an example of. 

So I think this another example of math being GRRM’s Achilles’ heel.