Here are a few options to consider:
-Have a “yard” sale for any one who might be interested. You can also send invitations to other gym owners in your area letting them know about the sale in case someone is looking for a type of piece from the equipment you are selling.
-I’m not sure of your location but you can check for stores that buy used fitness equipment (2nd Wind is one of them).
-You can donate them as part of a silent auction that will benefit a local non-profit organization. You will get extra exposure to potential customers/members and/or get business tax credit for the equipment you will donate.
I hope this helps.