Not a thousand miles of the 70 mark myself but generally speaking without getting too technical.
If money is tight I think your doing the right think, Mobile phone & Mobile broadband.
I'm a lite user too:
I have mobile phone with Tesco who use the 02 network, and every time you top up by €10 or €20 you get same value as bonus free credit.
Mobile Broadband is with meteor, and costs me €20 a month top up for 7.5gb data limit. In fact 2GB would do me per month, but they don't have a monthly plan for that low usage.
I'm happy enough though and can't find much better without going BILL PAY and i don't want that.
The signal is the most important thing first, but you can usually get a free 7 day trial with Meteor/3/Vodaphone and see who has the best signal in your area.
Can u give rough idea of your general location.