I don't normally recommend brands. You can consider Swanson as they usually have reasonable prices for both NAC and Quercetin.
The first consideration will be establishing the effective dose for NAC and starting at 600 mg~ 1200 mg /day as already established in other health issues. It will come down to trial and error. Not knowing exactly what is causing the allergic response, it is hard to know the answer to how long will you need to take them, but first you have to establish that these two supplements are helping. You already know the dosing for Quercetin.
Lastly, you might also consider adding Xlear Nasal Spray as it has both Grapefruit Seed Extract and Xylitol in it and can kill pathogens and breakdown biofilms in the nasal passages. Here is a link:
Let us know how you make out with these options.