The QBIS pricing system charges micropayments on a Pay as You Use basis, so if you only use 75 pence of service for a week, that’s all you pay!
You also don't have to pay anything to look at or amend any of your data in QBIS. So if you create 100 contacts, that will cost you a pound. But if you only ever look at them again, or just change them, that's free.
When you sign up for a QBIS account we will give you 2000 credits absolutely free, with no commitment or contracts. When you've used these up, simply top up your account to carry on.
For more information see the main QBIS pricing page on QBIS.net: http://www.qbis.net/pricing.html