PAYG or Contract?

If you use wifi for the internet then you can work out how much you would pay for texts. Check your providers website and see how much they charge per text.
But if you use mobile data for Internet this is quite pricey.
You might be better off getting a new sim only contract.
A lot of comparison websites compare mobile phone contract prices.

Try giff gaff they are very reasonable. First though look through money saving expert.com really useful advise on there.

I found Tesco very reasonable.

Ditto

My contract with EE was due to end next month. I decided, that as I was quite happy with my phone and did not need to upgrade, to change to a SIM only contract. EE wanted £10ish for their cheapest option, whereas BT was only £5. So I decided to cancel my contract and request an unlock code from EE. EE were very helpful and it would be no problem, but why was I leaving ?. I explained that BT was cheaper, I now have a £5/month SIM only contact with EE giving me more minutes that the BT option. The chap said there was no point in EE losing a customer to BT when the two companies were now one.
They also changed me over a month before the end of my contract, saving me another £20.

So if you are looking to change to SIM only, quote BT's price, you may get what you want without the bother of changing.