First of all, I'm impressed and pleased with the calm and well-thought-out replies.

For me there are certain key points:
1) It depends upon the malady in question, I would have no issues with spending $200-500 treating an RI (or other "straightforward" illness) in any of my snakes.
2) The value of the animal in question. I hate to say this, but it is a factor. If we're looking at something complicated or unknown (something involving perhaps lots of invasive testing or an exploratory surgery) I'm more likely to opt for a more aggressive/expensive approach on a very pricey animal than I would with say a male normal.
3) All of my "at home" animals get the same consideration regardless of species, meaning my Scotties get the same level of financial consideration for vet needs that any of my snakes do. Horse stuff is a bit different since I have medical/colic insurance on mine, so they get treated very aggressively (although like bcr229 said, age and performance level is a factor).