Pay as you go/Wi-fi compatible tablet

If you want cellular data, you'll have to pay a provider for that, and I imagine PAYG will be more expensive than paying a fiver a month for 1.5GB of data (which is also what I have, but with plusnet). The plan I'm on, is a 30 day rolling contract, so I can leave at anytime (not tied in for 12 months); I think that's the case with iD mobile too (which the other user mentioned). These plans also have smart caps. Basically, you can set an amount (for me, £2) that you're not allowed to go over per month. So, in my case, I can never be billed more than £6.95 per month (£4.95 for my base plan, +£2 smart cap).

So, that's one thing to consider, if you want true PAYG (look at providers like GiffGaff) or a 30 day rolling contract (look at Plusnet or iD mobile etc).

Another consideration, is to just use wifi. I do this option. I have data via my phone, and set up a mobile hotspot (wifi network) that my tablet can connect to in order to access internet while I'm out and about.

Hope that helps.