" not so expensive " is quite difficult in this area.

When do you want to go there? Most hotels offer in high season only full board or at least half board.

Will you have a car?

I personally prefer Forte dei Marmi, but there is nothing " not expensive ". But you should go there on wednesday, when there will be the market.

Lido di Camaiore, Marina di Pietrasanta or Montignoso should be your choise, if you want to stay near the beach. Take at least a *** hotel.

Pietrasanta is nice, if you want to stay a little bit away from the beach, but not to far away. There is a connection by bus or train to nearly every versilia location.