When importing you still have to have a "skirmisher" defence under VCRA rules. Be it UKARA registration or site membership, and be over 18 and fit any other criteria under VCRA for buying a RIF.
I have UKARA, so I ask the companies to put my UKARA number on the ouside of the box for customs. If you don't and they find its a RIF then they will hold the weapon and ask you to prove your defence as a skirmisher. If you cannot, then they will destroy it.
Then you have to look at import duty. Anything over £18 inc postage is subject to import duty if outside of the EU. You may also get hit by a handling fee of royal mail/parcelforce etc, which can be around £20
I have ordered from Hong kong, and Poland. Both take about a week to a fortnight. Both put my UKARA on the box, so I had no problems with getting the RIF's through. Poland is in the EU so had no problems with import duty. I tend to keep my orders from HK quite low so don't get hit for duty.
If you tot up the prices and use something like xe.com universal money translator then you can work it out. Work out the $ or EU to £, then multiply by 1.175% if you think you may get hit by duty, and add £20 for handling and see if its cheaper than buying in the UK, if you can buy the gun in the UK.
The other thing is that if you have a problem, they usually want the item returned to them which can be a hassle, so factor that in. Galaxy can be a bit hit and miss, so may want to try to get from UK, JG are pretty solid so I would happily order them from abroad.
Anyway there ya go.