New Amp Suggestions

I desperately need a new amp for my diamond 6.5" components in my tahoe and a buddy works at a stereo shop so I can get anything for cost or below. I have been out of the audio game for a minute as far as multi channel amps so would an alpine 4 channel or a diamond 4 channel be better? Or should I buy a 4 channel for the 6.5's in the rears/ rears and another bigger 2 channel for the diamonds? Diamonds are currently in kick panels and are powered by an older rockford that keeps making slight ground noise no matter what what I do, any help is appreciated.