Rolley,
It might depend on how you want to use the internet. I bought a Carffour Dongle when over in Spain earlier in the summer. It was on special offer at the time at 19 euro's, plus 5 euro's for the sim card. Pay as you go was then either 1 euro a day , or 19 euro's for a month (I think). It was much cheaper than anything I found available elsewhere. Uses Movil, which was piggy backing the Orange network so had no problems with coverage.
The paperwork is all in Spanish, but it really was simple & just a case of putting the sim card in the dongle and plugging it into the laptop & in putting a pin number, which was all quite simple. There are download restrictions, but we only wanted to be able to check emails and look at a few web sites, so it was more than adequate for that. I am used to cable Broadband in UK so have a quick connection here, but the dongle was not that bad for what we used it for. Might struggle if you wanted to download large files/music though.
It will be pot luck whether you will find a member of staff in Carrfour that speaks English, but by pointing at what we wanted on the leaflet available on the counter, plus a bit of pigeon Spannish, managed to make ourselves understood.
John