Update pricing details for monthly and yearly

[joncojonathan]

Gscan was throwing an error as the signup uses the old @price helper. After these changes, GScan is happy with the theme.

Note: I do not have a test environment for this, so would appreciate a review please.

#hacktoberfest

[joncojonathan]

I've managed to test the theme quickly on my blog (I had a file size upload limit issue before) and the theme loads in OK. Sadly emailing users is broken on my site (self hosted) so I cannot test the full functionality.