The monthly VIP is a subscription. You can only pay for it via PayPal, and it can be cancelled within the 30 days if you wish to stop the subscription (You'll still have access to the VIP rank for the remainder of your subscription). As
@milkified said, you cannot buy rank upgrades for the 30 day VIP. You also don't get monthly rewards with the monthly VIP, if I remember correctly.
Your best option would be to get a permanent rank if these are things that interest you, or you could use the monthly VIP as a sort of trial. The choice is completely yours.