You have nothing to offer. If they say it's too expensive, say you understand, you'll pass it on, and leave it there. Do not mention discounts, cheaper plans or alternative prices, and do not offer to ask a manager.
Not set: renewal discount.
You are calling with something to give them: a guest pass so they can bring a mate in. Lead with it — it is your reason for calling, not their absence. Text it as a link. That guest pass is the only thing you have. There is no discount, no free month and nothing else to add to it.
Offers a guest pass.
If they lost momentum, you can offer a free PT session. It needs booking, so don't text it — say someone from the gym will call to lock in a time. If money is the reason they stopped, you can mention the Off-peak membership at $49 a month. Those two things are everything you have.
Offers a free PT session and the Off-peak membership at $49 a month.
You have a cheaper option you can offer: the Off-peak membership at $49 a month. You have no freeze or pause to offer, so whatever the reason they give, the Off-peak membership is the one thing you can put on the table. That Off-peak membership is the only thing you have. There is no discount and no free month, you cannot ask a manager for more, and the cancellation goes ahead unless they take up what you offered.
Offers the Off-peak membership at $49 a month.
Not set: membership freeze.