I got mine done for under $1,000 at an independent. I had quotes of up to nearly $2,000. Expect a dealer price to push the limit.
Through fellow prime members, I found that the place I had mine done was very reputable and for this type of service so I felt comfortable. I didn't focus so much on the "dealer factor" since I've actually had trouble with dealers in the past (other cars, not my acura). I looked at if the shop had worked on a number of NSX's.
If you drop into Niguel Motors, you will likely see an NSX being worked on. Also the owner/mechanic (Ramon) owns one as well. I was told very good things about his honesty and quality work on maintaining NSX's. I had a great experience with him and have talked to several NSX owners that use him and everyone talks positively about Ramon.
Autowave in Orange county is also a great independent shop. If you drop by there, you will likley see several on any given day. There are a number of folks that ship cars from quite a distance to have them work on their cars. I believe they are the most experienced on NSX's and are focused on perfomance tuning in addition to maintenance. Their Timing belt change includes actually removing your engine and replacing a number of other items that they recommend at the same time while the engine is out and their is limited labor involved. This, of course, adds to the cost but also takes better care of your car and reduced cost long term.
If you want to get it done at the dealer, you might look into South Coast Acura. that is where the NSX-CA club meets every month and they offer discounts for parts and I'm not sure if that also applies to service. Because of their support of the NSX-CA club, they end up working on quite a few NSX's and would rate high in my book.
I would be cautious in taking your NSX to just any dealer. they may have deep pockets, but "Junior" that just came out of Acura mechanics school might not have been taking notes the day they talked about NSX's and you would hate for him to learn on yours. I would recomend one of the 3 above if possible.
All this being said, I'm not sure that a timing belt is the most complicated maintenance for your car and is fairly comon, so you're probably OK at all of these places. "Junior" could even do it with a good manual!! That is why I went for the low quote. I know the ramifications are high if its done wrong, but I think that is somewhat rare. Others might want to chime on this however since I'm also relatively new to the NSX crowd.
Ultimately, it comes to your choice and how much $$$ you can afford vs. your read on the dealer/independent factors. I would definutaly avoid just any dealer or independent. but eh above 3 are all great so you probably can't go wrong.
Good luck!