It usually doesn't cost anything to import them from Japan, customs rarely bother with items under $100. I think in all my time collecting tamas, I've only been charged duty/tax one time.
Edit: Couriers will charge you though, so stay clear of FedEx and UPS if you want to avoid extra charges
I think that might be different for someone living in Canada versus those of us living in the UK - I think that is why the question was asked (about Royal Mail UK).
I get packages from North America without paying import tax because they are a gift (private individual sending to private individual) and they are worth under £100. I've also had packages from Japan - low cost tamas - around US$35 - and not had to pay any charges.
If the tama is being posted to you in the UK from outside of the EU (like, Japan or North America, for example) it has to have a customs declaration form completed by the sender - including if the item is a gift / personal use and it's value.
The info provided will influence if you pay any import duty. Usually for items less than £135 AND intended for personal use / a gift you would probably not be charged. Or if the amount of tax due is small (less than £10) they don't charge you.
But to qualify as a gift it has to be something sent by a private individual (not a selling company) to another private individual.
It's complicated! You would probably need to do some research on the HM Revenue & Customs site:
https://www.hmrc.gov.uk/customs/post/buying.htm#3
(or google UK import tax and check out some of the links)
Basically, if your seller doesn't give a correct value (pretends it is very cheap) it can delay the pack in UK Customs whilst they check on what the real value is - and then charge you tax on what they decide the true value of the tamagotchi is - which might be more than it's actually worth!
Edit: Mostly I browse and keep an eye on the UK ebay / amazon sites for deals. It takes longer but cuts out the hassle of import tax and you just pay UK postage fees - extortionate enough IMO. If you have any family or friends in the USA or Japan who can get the packets delivered to them and then post them on to you that's usually the best route - but relies on a lot of good will, love and trust!
