DPD generally do the cheapest reliable international shipping that I've come across. I've sent all sorts of stuff around Europe using them. If I remember correctly, an Orange Rockerverb 50 Head shipped to Spain cost about £50, including the insurance.
Dave, for you, the best prices should be found by shopping around on ebay under "parcel delivery Sweden", to find an agent who is selling off "cheap" DPD deliveries.