Majic:
The problem with that is that unless you are loading those in a short barrel snubby, the snakeshot rounds loose their effectiveness against snakes due to the "donut pattern" effect. And if you really did need a HP round because of a 4 legged threat, shooting it with a sparse bird shot round will just make it madder. Ok, maybe you'll take out an eye, or hope that the pain of the birdshot and the noise will deter the attack, but that's about all you can hope for; I for one sure wouldn't want to bet the farm on it. Against 2 legged threats, you may find them somewhat better (added psychological effect), but even then I'd recommend against it -- you are still more likely to just antagonize the BG. While what you suggest may be a short term answer (better than nothing), I'd still recommend going the dedicated derringer/mini-revolver route for the snake shot.
Oh -- Scamp: keep in mind that you can cover both of those bases nicely and still stay within your budget. For instance, I bought my 4" 686 back in November for $300, used. If you check around, I think you'll find that you can beat that price. You ought to be able to pick up a somewhat lighter K frame S&W for about the same price. Likewise, you can pick up a derringer or one of those mini-revolvers, or even a cheap-o snubby for the snakeshot for less than $200. Combined, you are still under budget. I'd go with one of those NAA mini-revolvers, they are incredibly light, just the ticket for snakes.