Money-making Niches!

Of a problem product from my point of view. First off, the market you suggest is quite well covered by a couple of US web sites, but really my expertise is in utilitarian everyday instruments that farmers, industry and research use.
1.) The best collectors barometers contain mercury. In order to ship we need a hazardous certificate, or have them filled at the point of use. Either way adds (big) costs.
2.) Buying a barometer is a "touchy feely" event. I sell ten times the number of barometers over the counter than what I can sell by mail order. when I do sell by mail, they sell to industry type users who value accuracy over appearance.
3.) Barometers need to be set by the customer. A gauranteed recipe for returns, telephone support and problems.

Just on the topic of freight, the internet has not made it any cheaper to move actual things around the planet. Most of my goods come from Europe. By the time I land them, they contain an extra cost of 25% for freight and customs. Sending to the US by post will add more costs as well as aggravation complying with US postal regulations. Couriers will relieve the aggravations, but at a high cost. As an experiment I suggest you check how much it would cost to fedex say a laptop to New Zealand.