Sorry for the additional unwanted advice, but have you considered a pay-what-you-want pricing for the upfront fee? You can set the minimum to zero and a defaul

Sorry for the additional unwanted advice, but have you considered a pay-what-you-want pricing for the upfront fee? You can set the minimum to zero and a default above your target, and perhaps ask only after a short free trial period. I heard that it often yields better results than we would expect.