Samsung Galaxy S4 launch had already affected the strategy and the way of thinking of Apple, which had already scheduled its release of iPhone 5S, it remains to be seen whether Samsung will take over the competition and keep his way to the podium.
Most rumors say that the price will be the same that Galaxy S3 had it, when it was launched last year, in May (about 499 pounds), Samsung was forced to drop their prices, to keep up with competitors like Nexus 4, for example, so it will be the same with tomorrow's launch.
I you purchase the phone under a contract, the cost will be about 30-40 pounds per month, at least, but you will surely have 4G included in the subscription.
I personally do not imagine mobile telephony services outside a contract, but I use at full capacity the smartphone that I have.
However, for this phone, the cheap price will not be a strong point, and still it will be cheaper than the iPhone 5.