Doing that in a year or even six months is plausible, depending on how lucky his circumstances are, but three months strikes me as a bit of a stretch. At $10/hr * 40 hr/week * 12 week = $4800, ignoring rent, food, incidentals, and taxes.
Based on my friends' experiences, you often have to fight tooth and nail to actually get overtime at some retail or fast food places. In other words, simply working more is not always an option.
If that were to become an obstacle, one solution may be to get a second job.
And yet the OP writes that he's having trouble getting even one of these jobs. It may be hard to believe, but some small towns have a vast, vast excess of people wanting these jobs.
I can believe it. I'm from somewhere which is in many ways worse off than Yakima. That's just the best idea I have. If he can't make any money at all, I don't know what to suggest other than join the military. But I'm not a military guy, so I wouldn't feel comfortable suggesting that.
I could also suggest he goes off to western north dakota to work in the oil field, but I don't know if that's such a great idea. I have some friends that have done that. It sounds horrible, and they look like they are about 15 years older than they actually are. Plus you need the money to get there, and need a car, all of which is probably $5K+ anyway.
Doing that in a year or even six months is plausible, depending on how lucky his circumstances are, but three months strikes me as a bit of a stretch. At $10/hr * 40 hr/week * 12 week = $4800, ignoring rent, food, incidentals, and taxes.