Cheapest way to mail something to the UK?

I tried to mail a small box to one of my friends in the UK yesterday. It weighed 5lbs 4oz. The cheapest way to mail it cost $51!  I don't think the stuff in the box was even worth that much. I checked with FedEx and they wanted $120 to mail the same box. 

Does anyone know of a cheaper way to mail stuff to the UK?

I'm going to get a padded envelope and send about 1/2 of what I was planning on sending in that. (I'm thinking an envelope will be cheaper than a box?)

I usually send my stuff through the USPS since I can't find much cheaper with a courier My fiance's niece wanted some Lucky Charms since they were 8 quid or whatever over there, and her mum refused to buy them for her. Well, I thought to myself, it's only like, $3 over here, and it shouldn't cost that much to ship them, it's just two cereal boxes.

Right?

$20 just for cereal boxes--the Lucky Charms cost me $25 to ship to the UK. Never again >.<

I always send stuff by USPS. It just feels like in the year or two  the price of shipping has doubled.

I feel bad because one of my best friends over there is always sending me stuff, but I can't really afford to mail stuff all the time. She can still post stuff somewhat cheap. It cost her about 12 GBP to mail me a box a few months ago. 

I tried to mail a small box to one of my friends in the UK yesterday. It weighed 5lbs 4oz. The cheapest way to mail it cost $51!  ...

I'm going to get a padded envelope and send about 1/2 of what I was planning on sending in that. (I'm thinking an envelope will be cheaper than a box?)

The issue is the USPS got rid of overseas parcel post. Now everything is Priority Mail, which is an air service. This really increased cost. You can use the priority flat rate envelopes and boxes. These should save some money, but they are limited in size and weight.

The best way, IMO, is to use USPS flat rate envelopes and boxes.  They do not go by weight, but by a flat rate assigned to the particular box or envelope. You pick them up at the Post Office (for free!) and stuff them with anything you like (within reason)!   The envelopes, which do not have to be perfectly flat, and small boxes are $12.95 and can weigh up to 4 pounds.  Here are the rest of the prices: http://www.usps.com/prices/priority-mail-international-prices.htm

Thanks for posting that Mirrajay!  I've sent an email to my family to let them know!