Shipping it via the post office won't help. I've had small packages sent and they've also been charged. How likely it is to be charged is based on how much the declared value is from what I hear. If it's low then they don't bother as it's just not worth them doing it.
Royal Mail also charges VAT, import duty and a handling fee. So it's pretty much similar to what you'd get charged by FedEx. Annoying aspect of Royal Mail is that if nobody is around to pay the fees when it's delivered, they take it away with them and you have to go to their sorting office to pick it up. FedEx will leave it and just send me a bill later on.
It really depends on how busy the customs office is on that particular day...

- Trevor