I was told a check list of items to inspect/replace when replacing the timing belt
Water pumpTiming belt tensioneridler pulliesCam shaft sealsfront crank shaft sealall assesory belts
This is due to the labor involved because the same tear down is mainly required when doing these items
I paid $360.00 locally so that is not bad. The local nissan wanted $600.00 and infiniti wanted $1200.00
The timing belt is very important on this car. This is considered a zero tolerance engine. This means if the crank moves independent of the cams (when belt is broken) pistons will meet the valves and damge will occur and it is not cheap.
If you have the time and skill it is a diy job
The following is a reference on how to do it based on the sister car the 300ZX
http://www.ttzd.com/tech/timingbelttech.html
Do not use the part numbers in this article, call Joe at Scottsdale Inifinit
http://www.infinitipartsusa.com for pricing and numbers
I wish I took the time to do it myself because my great mechanic overtightened the assesory belts and I had to replace the ac tensioner pully a month after. At that point I became a true DIY except for major engine and transmission work
Now If I could only convince my wife to let me get a lift
Good luck