I have been looking on the 3 site but cannot see any offers for £2.50 per day?
Ugh their site is impossible to find these things on.
Its in the price guide, here (PDF download):
On page 8, you find the mobile broadband pay-as-you-go add on list:
1GB = £10 or 30 days whichever hit first
3GB = £15 or 30 days whichever hit first
7GB = £25 or 30 days whichever hit first
OR pay by the day - 500MB for £2.99 available for 48 hours, unless you use up the 500 megabytes earlier.
EE have similar offers on their 4G mobile broadband plans, either on a tablet SIM or a MiFi or dongle:
£3 500MB 1 Day
£10 1GB 30 Days
£15 2GB 30 Days
£20 4GB 30 Days
£30 10GB 30 Days
Hope that helps.
James BT Infinity 2
19/09/2012 - Sold 42/6 - Getting 49/8.5 - Sync 53 / 9.5 Mbps @ 470m approx
14 years of broadband (ntl: cable to BT FTTC) - Router: Asus RT-N66U - Modem: Huawei HG612 speedtest