I've bought a costume from a site before and a TON of wigs from ebay and never paid customs or anything on them, just the shipping the seller put on. this is most likely on the customs forms they marked it as 'gift' which is a regular occurance and say what is inside and the value so it's not stopped.
if something gets stopped and you have a customs fee or handing fee to pay which there isn't much you can do about it. the times I've had this happen was with band merch and i ended up paying parcelforce £26.
London MCM Expo May 2013
London MCM Expo October 2013
Current Project: Fai & Kurogane from Tsubasa
Past outfits: Neku (TWEWY), Grell (Kuroshitsuji), Matt (Digimon), Miyavi, Aoi (the GazettE)
Dream outfit: Zato1 or Testament from Guilty Gear