Nils
I would stay away from the small electronics stores in Times Square, Canal Street, etc.. They might offer what looks like a good deal but some of those shops are a bit "shady". Stores like J&R Electronics and PC Richards would be a better bet. They've been in business for awhile and have a pretty good reputation. You can Google them for locations and prices. Their sales staff will be able to assist him with the WiFi part. I'm sure he will have no problem getting on-line in New York City. Too bad you're not making the trip, we could have met for a beer or two. Stay well my friend.
B