Nissan wanted to charge me $150 for replacing drive belt for 2003 350Z TOURING model and $215 for flushing transmission and $110 for flushing coolanst. Is this resonable or should I look elsewhere?

Well the $150 for the belts, Your paying basically 100 bucks to have them put on. Belts are around 50 bucks. There are 2 drive belts on your Z.

The Trans flush thats interesting. Your transmission uses J matic Trans fluid witch is $14 to $15 a quart. A flush takes 16 quarts so that $240 just in fluid. UNLESS THEY MADE A MISTAKE (hint, hint) Most trans flushes are using matic D fluid. That is not the fluid required for your Z. If they use matic J for the flush. Then sure your getting a deal there.

$110 for coolant flush.. How many miles you have on your Z the coolant is rated till 100k miles, even though i think it should be changed at 60k. If you have over 60K on the Z then i would do it.

Take care..