Don't have people pay at all. You can make money by putting up ads (no sound, please).

What would be a reasonable monthly fee if the lifetime is only $30?

Maybe make it $5 a month which means $30 can get you 6 months or forever.

I wouldn't know how much to charge per month,maybe it would be every 3 months or 6 months aswell. I suppose it would depend on his overheads, the number of subscriptions to lifetime membership and what price people can and will pay but i do think that the $30 lifetime offer is a bargain.

For $2 per month, I'll lease you a jar. Put a nickel in the jar every time you play. Problem solved. I'll even let you keep the jar for $15+S&H.