To get an iPhone 5 16GB version you have to pay $99 down-payment and 24 monthly installments (interest-free) of $20/month. The 32GB version comes with a down-payment of $199.99 and the 64GB has a down-payment of $299.99; both with 24 monthly installments of $20/month. And T-Mobile is also promoting the iPhone without an agreement for $5 79.99 only.
You can subscribe to T-Mobile‘s contract-free plans according to your needs. For a single line plans start at $50 for a month with unlimited voice, unlimited text and 500MB data. Check T-Mobile’s iPhone pre-order page if you are willing to order one.