Looking for an iPhone 5 on pay-as-you-go - Cheapest place to buy one?

Preferably on Orange/T-Mobile. If cheaper on another network then please share. If you can pay off the phone on a monthly plan but not be on a contract, this would be excellent.

No one is offering PAYG iPhone 5 yet
There are some SIM free ones available

and to be honest there will be not much price difference
as the locked ones can be unlocked for 15 pounds - so why would they offer more than that as a discount?

as for a payment plan
- that is what a contract and small (50-80 pounds) upfront cost for the phone is.
The phone is never 'free' you are paying it off over time.

- A credit card or overdraft.

A SIM free + SIM only contract (even PAYG SIM) can work out cheaper
'if' you are a low call/text user, even if a data users
- 15 pounds/m Three ultimate contract = 525 phone + 360 (24 months) = 885
less than a similar plan with contract (some 950 pounds)

Why?
Maths and Economics
Say eg £20 PER MONTH TOP UPS, ADDS £480 to £529, 16GB IPHONE5
Over £1000 for what is a Dual Core phone

What do you think you are getting?