Sounds like your not having much fun. Your life out there reminds me of "Driving over lemons". I presume you've read it? I suppose it's a life which is supposed to be far from the world of headaches of modern life and 3G internet!
When you say GSM 4/5 what do you mean? Are you talking about bars?
Have you tried the Yoigo SIM in your 3G modem in your area? They use Movistar, so in theory that should have the best 3G coverage.
It will work out a lot cheaper than the 50 euros you waste on Vodafone.
I'm sure we can work something out. There has to be something that will work.