Do you know anyone who is using one near where you will be moving?
They are like mobile phones - some work better in some places than others.
Have a look at the 1 month contract ones from 3. Here is a link and I can tell lots of people on here use them.
3 Store - Mobile Broadband
Look at the top one £9.99 for the dongle and then pay £15 for 3Gb download for a month. After the month if you still need it just pay another £15. If you don't stop using it.
That is possibly the cheapest for you although a few people have had a few connection issues with those recently.
Personally I have a Vodafone one for occasional use. It is about £35 to but and then £15 per Gb used. I like it because it does not expire after a month if you have not used it up. I have to connect once every 3 months to keep it active. I use it rarely so is good for me.
I pay 3 times and much though for my bandwidth compared to the 3 one but my £15 will last me months the way I use it.