RE: Horizon Hobby charges sales tax for online orders???
If the company has an established presence in your state, they have to charge your state's sales tax.
HOWEVER, there has been a lot of work going on behind the scenes in the various levels of government, because they're losing a lot of money on sales tax due to online shopping. Illinois could be very well be one of the first states to adopt a law that you have to collect sales tax no matter where the buyer is from.
Frankly, it's only fair that we should have to pay the sales tax of the state we buy something from... If you drove to Illinois and bought that stuff from a hobby shop, you'd pay Illinois sales tax.
It's a good thing for local hobby shops. Most hobby shops match Horizon's prices, but local sales tax versus shipping, shipping usually is cheaper. If you had to pay the seller's state sales tax on top of shipping, you'd be more apt to buy locally.