Changing the membership subscription amount

I want to charge varying amounts for a monthly, 6 month and annual subscription. The largest amount the subscription plan allows you to pay is $300 and I need to charge 377. Is there a workaround for this?

Also can the periods be changed from days to months? Most subscription plans are run on months and they bill the same day each month. If someone is paying 20/month for a subscription, on a month basis its 240/year. Using 30 days is 13 payments for 260/year. Just a little thing but something I don't want to have to explain to my subscribers. Every other membership is monthly; gyms, clubs, teams, etc.