A rough average wage for a laborer around this time was $1 a day. Farmers of course would have good and bad years, but if you assume someone with decent acreage, it's not too big an assumption that he would be making, much of the time, at least that.

What could he buy? Sears catalogs show a lot of guns could be mail ordered. A rifle or shotgun would be far more cost-effective than a pistol, for keeping the varmints out of the fields and bringing home something for dinner. A simple shotgun could be had for $8, a Winchester rifle for $10, so both were within reach of his finances ( he could, of course, pick up something used for less). Shotguns are perfectly good things for defense- and one could assume that, like most people, the farmer would seldom need a special gun for that, and so would first buy something practical.

If he got a pistol, it might not be a Colt, though. Michael Piatt's history of the Bodie CA mines occasioned a close look at newspaper accounts of crimes in the area, and he discovered that , instead of the classic Colt Single Action Army, there were a lot of cheaper pistols employed, along the lines of the cheap and concealable "British Bulldog". For good reason: a Sears catalog of 1900 shows the price for the Colt was $13.20, more than the Winchester rifle or the basic shotgun, whereas the Bulldog could be had for only $3. So, if someone poor wanted a pistol for protection, he probably got something that you wouldn't see in a movie.

EDIT I only address the basic question as to whether he could afford guns: he likely could. I am not claiming that Idaho farmers did not often own pistols, even fancy ones, in 1885: someone may actually have definitive data on that, I don't. Cost effectiveness is not always the perfect predictor for what people buy, whether it's 19th c. farmers buying guns or 17th. c. Dutch buying tulips.