I'm glad you're interested to sign up for QuickBooks Online, valimh! I can help you get the discounted price.
You can open this site: https://quickbooks.intuit.com/uk/. Then, click on Buy now & save 50% in the Essentials section. If you're still prompted with £18, please call our sales team using the number in the upper-right hand corner.
We have some articles about QuickBooks that you can refer to in the future.
Please let us know if you need more help.