Sometimes you can get an unlimited data for a week offer with some EE pay and go sim plans, not sure about what offers Vodafone has right now.
you have to text to opt in if you are eligible worked out £1 daily for unlimited calls, text and data but this offer pops up randomly as part of its loyalty scheme
The signal is too weak to penetrate a lot of buildings so you need to go outside or near the front door,
if you could use an antenna that is already there to forward the signal to your phone maybe you can increase the coverage area for your phone only.
people are complaining these phone signal repeating devices when setup properly give slow mobile internet compared to the normal phone signal but because you would want to use this to bring signal to an area with no signal whatsoever that wouldn't be a problem,
and i believe that is down to the device itself being a bottleneck for speed