Sign up for O365. £7.99 a month or £79.00 per annum and you’ll get the very latest version.
Sod O365. Subscription models for your average home user are just not worth it. Nearly £500 over 5 years… you’re ok thanks.
+1 for buy a licence key – I’ve not used Softwaregeeks, but eBay is a rich source – plenty of 2007 ones on there for £1 or £1.50, or get 2016 for £10.
If you don’t need Excel specifically, you could try LibreOffice or OpenOffice – both free and very good – can open/edit Excel stuff without issue.
As a competent Excel user I found both immensely frustrating (although not as bad as Google Docs), all the keyboard shortcuts are different, nothing is quite where you want it to be. It’s 95% of Excel, but the 5% is utterly infuriating.