>Usually taxes are percentage of the value of the import. Where do you get those 250$

If the sending country doesn't collect customs duties for the US, then the US will place a flat fee of $250 on the item regardless of its value.

>From EU it never made sense to buy anything from small US business, with the absurd shipping costs and VAT.

Perhaps in your case, but some products are specialized or of much higher quality than can be found in the USA.