Will Vodafone reduce contract prices of iPhone 5s once 6 is released?

I'm due an upgrade and was going to get an iPhone 5S as I'm not particularly bothered about the iPhone 6, mainly because it's so expensive.

Am I better off waiting until Friday or will the price of the 5S stay the same even once the iPhone 6 is released?

It may go down a bit, but probably not much. It's more likely to go down in a few months time because there are probably loads of people who, like you, are waiting for the iPhone 6 to get released and then get an iPhone 5s, thinking it is cheaper. I just checked the monthly prices on both the iPhone 5s and the iPhone 6 (not the 6 plus) and the lowest monthly price is the same for both of them.

You could look on eBay, because you can easily get a new one but there are usually refurbished ones instead, for around £300.

I would say wait until Friday, and if it hasn't gone down, then wait a few months if you wish to. It really is down to luck and whether you are good at being patient at waiting. You could be wasting time by waiting because it may not go down for ages (maybe even a year) or you may have some luck, and vodafone decreases the monthly price on the iPhone 5s.

Bear in mind though, that with an iPhone 6 you would get a year longer with running the latest iOS than the iPhone 5s, because it is a year younger and there are about 3 major iOS that each iPhone has got, before it misses out on more of them.

Hope I helped!