I think most do--I know Motion does. But I believe it's $20 per visit (whereas I pay $75 per month for full membership. If you just want to use the treadmill I might look into Eastside. Their membership is already pretty inexpensive but I'm not sure if they offer anything by the month or visit.
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Do any local gyms offer a pay-per-visit option? I'm just looking for somewhere to go a couple of times per month on the weekends if it's too rainy to run outside.