A lot depends on what type of ammo you are looking for.
Best deal on CCI Mini-Mags seems to be Wal-Mart. Similarly Rem Golden Bullets for HV .22LR in bulk packs of 550 for ~$20. They work well in my Glock/AA Conversion kit and 10/22.
I use Aguila Std Vel .22LR for handguns, but I got that via CMP a few years ago. I see it in stores occasionally but can't point to where.
For gun shops in VT, I know a couple of good folks (took a defensive handgun course with them) from John's Gun Shop, 447 Brooklyn St., Morrisville, VT, http://www.johnsvtgunshop.com/
and got a decent deal on some mil-surp rifle ammo last year.
VT has a sales tax.
For NH, the two big guys are Riley's in Hookset, NH (they also have a police supply biz in the building behind the gun shop, but it's only open normal M-F biz hours, unlike their gun shop that is open 7 days/week). The other one is Manchester Firing Line on Brown Ave., Manchester www.gunsnh.com
Enjoy your trip. And if you run into Ron Glidden in S. Wellfleet (he's retired and moved there) say hi for me.