Buying local versus buying online; where do you draw the line?

I prefer to buy my things local and when possible from a smaller store and not a chain but sometimes the difference is too big to swallow. I priced up an item locally that is $840.00 plus tax. I can get it online for between $412.00 – $525.00.

For me this is too big of a difference not to purchase it online. A 40% plus markup for the same item is too big of a difference in my opinion.

Where do you draw the line? 10%, 20%, 32%? Or do you consider the dollar amount more than the percentage?