Yes there are some good local fish stores that are smart and truthful. I would read some reviews online and look at the more local stores instead of big corp ones like petco. The maw and paw stores are almost always more passionate about their hoby.
When I set up my first tank I bought everything bran new... big mistake and a waist of 600 bucks. Used tanks can be bour at a dollar a gallon and tones of decore. Craigslist or local ebay searches work well for getting great gear at a fraction of the price.
I see one potential problem. If you follow the book and get him a tank for xmas then normally it takes about 6 to 8 weeks to fully cycle. Not sure what your knowledge level is on the nitrogen cycle and biofilters and I can explain pretty easily if you dont.
You can take steps to get it running sooner I just want to make sure patients is something you son has or at least something you would like to teach him.
If you would like help learning this or looking for some good places or gear online please just let us know and tell us what city and state your in and we can look up some craigslist items and LFS
(local fish stores) for you to check out.