I spent 300 on my set up, I have the stock mach 460 and just added a 12" Kicker Comp CVR in a small sealed box with a Performance Technique 1200watt amp. I only wanted more of a full sound so I don't turn the amp more than 1/4 of the power up, anymore than that and it overpowers the stock speakers.
For your set up...check and see what the rms watts per channel is on your kenwood head unit. That is the sound you will hear all the time, the 45 peak watts are what it could push out at just one time...the rms number is how loud it will sound constantly...anything more than 20 watts rms inside your car is enough to have your ears ringing for a while. If that's not enough for you, and you want the whole block to hear every word said in your music, I'd either add a 4 channel amp to power the inside speakers, or get a head unit with more watts per channel...
remember your speakers are only as good as whatever powers them...so even stock speakers sound better with a better head unit...