Just wanted to add my 2Cents on this.
I'm currently rebuilding my CJ-7 and so have to order lots of parts in the US, it's WAY cheaper. There are different ways to get them over here. All this is what I experienced here, backed up by a fellow from the customs office who told me details over a pint of beer. Some details may vary between countries but the general tendency should be good (or rather bad).
USPS
US Postal Service is the cheapest one but takes its time. They have a rate for a box up to 20lbs in a normal size for 35$, air. And you get a tracking number. Not that it shows much. Will get taxed regardless of value.
www.usps.gov
UPS
Faster, way more expensive on small parcels. Something BIG as a pallet exceeding 500kg gets you over 1000$
Fed-Ex
Priced similar to UPS but small boxes get through the customs without being taxed. Seems to be too much work. So they are about a week faster than others.
Mail forwarder
There are several companies who group different boxes into a large package. This is THE solution if it says "US adresses only", "lower 48 only", "no PO boxes". It's also cheaper to regroup.
Customs
This is regulated for Europe in a common way. First they add custom duties. Those vary widely depending on parts. Some pieces may be charged 0%, or 3%, others 10 or more, depending on what it's labelled and where it came from. Have a look at your local customs, they have surely an online list of taxes. The value of the part is taken PLUS the shipping cost. A box under 200€ should not be taxed but this depends apparently on the carrier. They get a fee for doing the docs, so some do every box, others just large parcels.
Sales tax
or whatever they call it in your corner of the woods is added on top of this all. Varies from 16% to awww-my-god depending on the greediness of your gouvernement. Calculated on parts price, shipping and customs.
Ebay
Problem is that you often have no real bill included. So they accept any prove of the value, like a printout of the completed auction or a Paypal printout. If the value looks too low they check this. And they may even charge you a guesstimate of its real value in case you bought it for 1$. So if you buy a set of fuel injectors for 1$ they call the official stealer and ask how much he charges and take this as base for taxation. Oh, sure, you can try the legal way but does mean the box stays at the customs for 2-3 years until it misteriously disappears.
Gift
Not good. A gift without value which contains "valuable" items will be treated in a special way. Don't try this.
Important
If you get a box that contains other parts then those stated on the bill that comes with it you are in deep doo doo. Even if it's only some shirts and a cap. If you are good and they are friendly you can talk your way out of this. But more likely they will keep the box until the matter is settled or simply send it back to sender.
Also make SURE a bill is specific for each shipment. If they drop off a shipment of 2 boxes and each one has a copy of the bill for all the parts and they get separated on the way than you will get taxed TWICE until you can prove it to a customs officer. Which isn't easy. Ever tryed to turn a mule on top of a narrow staircase? That's easier than convincing an official.
Hope this helps anyone.
Regards
Alain
Luxembourg