The Broncos have retained a bulk of their roster and will add NSW star Jack Bird to their squad next year meaning Marshall will once again have to accept unders to remain at Red Hill.
"There's room for Benji, but we just can't afford to pay him what he's worth on the market," Bennett said.
"We have to put our money into place with our younger players and we've done that. We can't afford to lose him.
"We brought Jack here and we can't afford to lose Kodi [Nikorima], we can't afford to lose Jordan.
"Hopefully, Benji will stay - he's happy here, he loves being here, we love having him here."
Marshall has opened talks with Brisbane and Bennett confirmed he would like to give the 32-year-old another season.
The Kiwi veteran started the season in Queensland Cup, but has added depth to the Broncos roster as a back-up to halves Ben Hunt and Anthony Milford.