Lexus 2011 GS350
 

Hi All,
I own 2011 Lexus GS350 AWD. Car has very low miles (84k).
Been running into some issues like Alternator, speed sensor, shock replacement, and brake caliper seized.
I took to the dealership and bill is around $5.5k to $6.5 K for everything.
I need some advice on some off market (non lexus brand) alternator, break sensor and others parts of replacement or shall I buy the parts from delaership and get it replaced from outside?
I cannot afford to spend so much money.
Any help will be really appreciated.