Adding a data package to your mobile phone

[Big G]

I'd like to get a smart phone, but I'm not sure about adding a data package onto my existing plan. At the moment I get 200 mins and unlimited texts which is great for me, but they bum me if I use the 'net' on it. I also pay £17 for this which is good I think.

If I got a smart phone obviously my data usage would increase. Does anyone know roughly how much they charge you for their normal 750mb data when done like this?

I'm on orange. I would take a upgrade, but I'm not due until March and buying the phone sim free works out the cheapest without getting locked into a 24 month contract at £35/month