Do you have to pay for a development in resources or are they free to play one each turn?

No developments are free. You simply play a card face-down from your hand in whatever zone you wish to develop. Just remember you can't play more than one development a turn unless you have another card effect in play that allows you do so. (For example City Gates forces you to play the top card of your deck each turn as a development but this doesn't count to your one a turn.)

Thank you. That helps.