We finally decided for a spanish company to do the moving. They have several options in order to get a good price. Namely, to make the moving grouping it with other people or being flexible with the dates.
Up to now our things are in their way to Basel, so I can't tell you if everything went ok or not. We'll see. Whenever I have some feedback I can post something here.
The company was Grupo Amygo, and it costed us 1515 € for 7 m^3, including customs and insurance of around 8000€.
Regading selling and re-buying here in Basel, keep in mind that the prices are not the same as in BCN (the salaries neither, though
). Ikea is more expensive here than in Spain (but is still the cheapest around). Otherwise, there is also a good second hand market, where people often gives away things for free. In our case we just moved personal things, books and things that are difficult to replace, and got rid of almost all furniture.