I am a frequent traveler between Bend and Boise. There are two options I would consider in heading home if you are interested in making good time.
1. I-84 to Ontario then 20 to 395 to Lake View. Between Vale and Juntura 20 follows the Malheur River. Though 55 zone (all rural roads in Oregon, except interstates are) I set the cruise control in the Prius to 62 and ease off a little on a couple of curves. After Juntura sight lines improve an I reset the Cruise Control to 69. I have been "caught" by radar several times by state police with no interest. (My son in law got stopped but no citation at 71). There is always a chance of a county mountie having a different standard (one did turn around and follow me a couple of miles but I slowed down and he lost interest). It is really strange but I have never traveled 395 between 20 and a few miles n. of Valley Falls. But it will be a combo of sagebrush, relatively low ranges, and some volcanic terrain. The Abert basin should have some water this year. On the opposite side of the highway is Hart Mt. Wildlife refuge and there is the possibility of spotting some Big Horn in the area. The campground at the refuge with a nice hot spring is about 40 minutes off the Highway and you have a good chance of viewing significant numbers of Pronghorn. (The Prius can handle the well graded road to the campground/hot spring but some campsites might be inaccessible)
140 from Lakeview to Kfalls is an interesting road but not the only alternative you have after Lakeview.
Plan b on this route would be to stay on 20 and pub crawl in bend! (let me know if you chose this and if we are home would be happy to show you around and lift a few!)
2. Even more remote than 20/395 is highway 95. Going through Jordan Valley and the Pillars of Rome near the Owyhee River is really neat. You really have to appreciate basin and ranges in Eastern Oregon and N. Nevada.
Oh yes. Consistently the cheapest gas in the NW is Boise so fill up there. If heading w. on 20 top off at the Sinclair station in Vale (I know only 1 gallon or so but it will be at least .20 per gallon less than anyplace else in Oregon outside of Portland and they have clean restrooms. (my wife gets really pissed

Cheers
Mike