Hope you get lucky with the import VAT & RM handling charge as HMRC are getting a bit too efficient these days as they reduced the personal import level to a measly £15 though a 'gift' is still £40
Problem is that most ebayers think it is a federal offence in the US to under declare value of goods, it is actually the consignee (recipient) who is responsible but most ebayers won't under declare anyways.
Frankly unless you include inside/leave an invoice on the front of the package it would be difficult to prove the value without one
If it does get picked up expect 20% VAT on declared item value PLUS shipping costs PLUS RM handling charge of £8
So for instance if they declare £60 equiv and it costs £75 including postage, that would be £15 VAT +£8 handling charge, so £23 extra.
Just so you know in case it doesn't slip through, fingers crossed.