This isn't an uncommon situation at all. First step is to ask yourself which cellular data providers are available in your Spanish town. My wife's aunt had to do something similar in Provence/France when her home DSL connection went bonkers. Smartphone was a very convenient backup.
Once you figure out who the provider is, then you quick hop on the online charts listing frequency bands by provider/country, so you know which handset will work where you will be staying. At that point we can help you determine which handsets that your propose would work. It's hard to recommend one since we don't know which ones you have for purchase at your current location, etc.
You might actually wish to obtain an LTE handset too, since there's now LTE there, at least with Orange and Vodafone on band 7 (2600MHz).
http://ltemaps.org/home/country/spain
This unlocked Nokia Lumia 635 (or something similar w/ a little more global LTE capability than 2600) could suffice.
http://www.amazon.com/Nokia-Unlocked-Windows-Quad-Core-Smartphone/dp/B00KM10ITK/ref=sr_1_19?s=wireless&ie=UTF8&qid=1427745030&sr=1-19&keywords=nokia+lumia+635
If you are in the UK, this would be the one to buy for Spain/Europe-
http://www.amazon.co.uk/Nokia-Lumia-635-SIM-Free-Smartphone/dp/B00KM10ITK/ref=sr_1_5?ie=UTF8&qid=1427745304&sr=8-5&transaction=device_only&keywords=nokia+lumia+LTE
I'm sure there are some Android equivalents though, but it may take a little digging on your part. LTE is mostly 800/1800/2600 in Europe, so those are your target LTE frequency bands for whatever you end up with if it's the full monty.
I visit Spain for about three weeks, twice a year. There is no internet cafe in our village, but a good 4G signal. I need to access my internet while I am there, using a data service which I pay for when needed, but which will not expire before it is next used. I would consider buying either a USB dongle for my netbook, or an inexpensive smartphone, but I don't know where to begin. Or am I looking for the impossible?
Many thanks, Alec.

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