Am going to change out my OEM Y pipe (has a leak in the flex pipe) for an aftermarket one. Advice on what to get? Looking online, they go from $100 to $300 give or take (without getting too crazy on the high-end ones).

 

Motordyne (but I'm biased ha). The one with the resonator will help with rasp.

Another route you could go that is cheaper (full exhaust under $1k) and popular with the Z guys is ISR. They make some nice stuff.
http://www.isrperformance.com/exhaust-13/

 

I had that same issue with my stock Y pipe. I went with one of the cheap ebay options $100 (Blackhorse Racing). I noticed a real nice improvement in power with this Y pipe, but the sound of the exhaust was ugly (tons of rasp). After that I changed the rest of the exhaust after the Y pipe, and now its not as raspy, only between 2-3k Rpms. But then again I have z1 Test pipes, so maybe with some hfc's it wouldnt be as raspy. Something to take into account is that cheap ebay type parts are going to be thinner metal, and it will affect the tone you get. Ive read that mixing brands of exhaust parts also leads to bad results on the sound of the exhaust. Also read that using heat wrap on the exhaust parts can change the tone as well. Im going to be trying some heat wrap on my test pipes and Y pipe to see if it cleans up the rasp I have.

 

Let us know how that turns out. It worked on my car for my ART pipes.