We're currently using 2 sims.
> A 15G/month EE data only rolling contract (we can duck out with 30 day notice) for £20.
> a Simyo (spanish company) data only 4G prepay card - 30Gb for 28Euros, we just chuck 28 Euros on occasionally and get 28Gb of 4G that lasts (iirc) 3 months.
Both cards are fully roaming (in EU) for a reasonable cost.
EE (allegedly) only allows 15Gb of roaming per month (other UK telcos are similar - 3 currently only allow 12Gb).
Together that gives us the ability to burn through a Gb a day - which we actually seem to be doing. We both "work" online and use a Huawei E5577 with a MIMO arial (
https://www.motorhomewifi.com/product/4g-huawei-e5577-mifi-window-mount-antenna/ ) for most of the access.
Funnily enough this tends to give us a faster connection than a lot of household broadband connections in rural France (we're doing a lot of house/dogsitting)
We also both have EE mobile accounts with some data allowance and full EU roaming - mine has 10Gb/month, the wife's is (iirc) 2Gb a month.