I'd say about 400 and up or so- that would get you a current refurb or a last years model with full warranty receiver that should be able to handle the NHT's I would look at Denon, yamaha, or onkyo. Maybe you could score a refurb Marantz for that.
How much music do you listen to? And what types? Do you have have a need for a subwoofer ?
you could check out amazon.com for the non current models and accessories4less.com for refurbs.
Pioneer is also a quality receiver but their GUI isn't as intuitive as the others from what I understand.
here are some possibilities:
1. Onkyo txnr-709- 400 on A4L
2. Denon avr-2113 - 450 on A4L
3. Pioneer vsx-1122- 380 on newegg.com
4. Marantz SR5006-500 on A4L
5. Couldn't find a yamaha that I would be comfortable recommending in that range.
A current new receiver would be at least a couple hundred more.
There are some great resources on audioholics university that will help guide to a decision as well as other posts in the amps and receivers forum here and the beginners section.
have fun ant take your time.
Cheers, Mac