What kind of dog (i.e. terrier or german sheperd) is good at detecting
snakes (especially rattle snakes) and alerting you that it has found
the snake?
My location: Texas Panhandle/High Plains (Borger area)
Prairie rattlers & bull snakes are almost the only kind of snakes in this area.
I would prefer a dog that did not need to be trained, but am open to
any kind of dog.
The dog would need to live outside.
I live in the country, so the dog would have plenty of room to roam. 
Cattle live in the area, so I would prefer a dog that does not tend to herd cattle

Nobody is touching your question. Let me guess, if you make the reward
at an even $20, many bodies might be seduced to at least ask you for
some clarifications before they, or one body, might give you an
answer. Fifty cents is big for these guys.

So, maybe, I give a comment.

Another reason you are not getting any nibbles yet is maybe because
Google is mum about them kind of dogs too. Maybe there are no such
dogs alive. Otherwise Google will include in its gazillion-item
records even only two or three sentences re them dogs.

I am sure, in the past, some dudes tried to train dogs, any breed, to
specialize on rattle snakes. Like find them rattlers, sniff on them,
etc.
I am sure, or perhaps, none survived. No dogs survived. Rattle snakes
cannot be bothered by any sniffing, snooping, spying, (meddling!) dog.
One bite, by the snake, and that was it for the dog. [I think the
failures were due to dogs not understanding the meaning of the shaking
tails of them snakes. Maybe the dogs thought them snakes were
trembling in fright at the sight of them dogs. So, to scare them
snakes more, to impress the trainers, them dogs tried to nudge or
dislodge them hapless snakes. Swoosh! Ping! Dogs dead in minutes.]
I am sure some enterprising trainers tried it on de-fanged or
de-venomized rattlers. Still, many of the dogs failed, not by dying,
but from bites on their noses or just even smacks on their noses by
the toothless snakes. Those who passed the training, once tested on
real, wild rattlers, one bite and dog dead in minutes.
I am sure the trainers lost money on too many dead dogs. 
I am sure the more enterprising trainers tried noseguards, or even
full-face guards, like screens/sieves/mesh, on some dogs. I am sure
those did not work. What dog would welcome such contraptions? Who
could train an unhappy dog?
I want to say I am sure the trainers quit on the business.

I am sure you know I am not really sure.

I am a dog trainer in England and have trained many types of detection
dog. Narcotics, Arms, Mines and Causality.
Most breads the Services use eg; GS, Doberman, Lab's, Springer?s can
be trained for most detection work. BUT. Out of say 100 dogs on a dog
purchase only 30% would be useful for detection work. If there is a
dog sniffing the air and not barking, it?s a good chance it would make
a good ambush dog. If on the other hand there is a dog sniffing the
ground and showing signs of wanting to please, it could be put to good
use on groundwork. Say there is another dog that lunges out on the end
of the lead at a person baiting it, then you probably have the makings
of a attack dog.
What I am saying is get a good dog trainer to find you a dog that can
and will detect danger from a distance, "pointer" or such like. The
dog will point in the right direction then its up to you to either
keep away or go get the blighter. (the reptile not the dog, he should
still be at your side)
So lets recap not a ground sniffer, not a barker. An air sniffer would
do nicely, one that does not lunge forward, one that indicates danger
to you by pointing with his whole body and nose.
Any good trainer with the right dog could succeed.

When we lived in Pakistan we had a mongoose kept around the house. I'm
a doggie person, but know of no breed developed for snake detection or
such