Complete audio upgrade for my 79 Corona

[79Corona]

I currenly only have the stock AM/FM stereo with two front speakers installed. The car is prewired for four speakers. The front kickpanels have 4" shallow speakers and the rear deck has provisions for 5x7 speakers (bottom-mount, I'm told). There is also a provision under the head unit for a separate Toyota cassette deck in a plastic console. The size code for the stock head unit is S,U.

Any ideas? I would like to keep the total cost below $350. I like the Pioneer and Kenwood head units, and Infinity, Kenwood or Polk speakers seem pretty good.