[andy]

I think buying a mifi would probably be better than renting at those sort of prices. And local SIMs would work out much cheaper than any of the roaming options you mention.

For data in England and Northern Ireland, you might a 3 data SIM with a gigabyte for a month for about £10, or a bit cheaper on eBay or Amazon UK

I think I read of Meteor being recommended recently here for data in Ireland.

Or yes, a phone instead of the router. Some monthly option bundles here allow tethering, some not. There are also cheap international call options on most networks.