Well its a bit more complicated then that.
Just cus you go no contract doesn't mean you cant get a phone for 'cheap.' On contract you pay a subsidy that is included in your service price that you pay per month. This makes for a moderate up front cost with a moderate monthly payment.
You can go no contract and pay for the phone outright and have a huge up front cost but you spend less per month.
But there is a third option. You go no contract and installment plan. Depending on your history with Tmo, they can give you a credit line so you can pay off a phone for 20months. This way its kinda like the best of both. You dont have such a huge up front cost, and you may not pay as much per month on the contract plan.