In small states like WV and MT, the power of incumbency is significantly heightened because a much larger percentage of the electorate has met with the senator, has received constituent services from his office, or else has some familial or business connection directly to him. So in those states, incumbency is generally going to carry over partisan identification. And no amount of money is going to change those personal connections that Manchin and Testor have in WV and MT, respectively.
As to Ted Cruz, you're just dreaming if you think there's a "moderate" Republican out there who (1) would challenge Cruz in a primary and (2) would win. But even if there were, I don't even know what a "moderate" Republican looks like today? Is that Joe Strauss? Well guess what--he ain't running for shit. And even if he were, he'd get killed in a primary.
Ted Cruz is the perfect representative of the Texas GOP. There are no shortcuts. If you want to beat him, you need to beat the Texas GOP.