Inexpensive Shipping to EU

Hey Folks--could use some advice. I have a box containing some audio equipment parts that I want to ship to Portugal. I went to the local Fedex and UPS facilities but they are quoting me $500 to ship a box full of parts that are not worth anything close to that amount. The box is roughly 20w by 12h by 20d and weighs approximately 50lbs. Is there an international shipper that you could recommend that will get this to Portugal on the cheap? I'd spend $200 if necessary but would like to send it for less. Suggestions are appreciated.
A big box and quite heavy. That is the high cost factor, not the value of the items inside. There might be a way to ship by sea, not by air.
USPS Ground cost me $150 for around the same to the UK. Beware of customs delays and payments on port of entry.
Yeah, USPS. DHL would be expensive but might be less than either FedEX or UPS. I like DHL.
Don't know much about this company, but heard it has good rates and it looks legit 

and the calculator is quite handy, you can check the price right away
Thanks everyone. After all that running around trying different carriers the best price was to be had with USPS. It went out today.
I received quite a number of bought records from Japan via DHL. Very fast and reliable, excellent on-line tracking, and the packages looked as if they had not been even touched, well except for some dirt outside.