Drfc56
My brother lives in Spain and had internet contact via dongle which connects to the mobile network. I think it was with movistar and it cost about 25 euros a month but that was under a contract. I am not sure whether the mobile networks in Spain will provide a cost effective way of using the internet through your laptop for 3 1/2 weeeks, even if you changed to local sim.
I would personally use the free hotspots where available or if not there will be internet cafes or hotels with facilities. In the small town where my brother lives, there are 2 cafes with fast broadband connections. The connections are so quick, that the cafes are very popular with the locals who prefer to use these, rather than the slower internet connections at home. They have about 6 PC's all with web cams/VOIP so the locals can sit there for ages. That is the only problem, gaining access.
Huckster