i really think that your estimate is way too high.
engine tune up parts would cost you around 500-600$ while suspension and brakes, including new shock absorbers, new brake rotors, new pads and new shims would cost you around 1k.
since both engines are the same it should cost you the same amount for the sc as for the ls. not sure about the brakes and suspension but should be around the same price.
labor charge to change the timing belt is around 400-500$. rotor and suspension change should not cost you more then 300$ per car. so total should not be more then 4k for both cars.
if mechanics are estimating more then this, then they are trying to rip you off.
get the parts yourself from an online store, then bring them to mechanic and only negotiate labor charge.
this will def allow you yo save a lot on the maintanence:)