In MemberMouse, you can set limited payment plans in the Product settings for an item.  You will place your monthly payment amount under 'Price', click the box under 'Subscription' and set the rebill time period you want.  Then, to make this a limited payment plan, check the box under 'Payment Plan' and enter the number of payments you want in the short text box.  For example, to create a $300 product, spreading the price out over 3 monthly payments of $100, your settings would look like this: