Most of the features in Diarly are free, but to have access to all options, you will have to purchase a subscription. The subscription cost is about 1.25$ a month (15$ a year) in the USA (might be different in other countries).
Premium Features Include
PDF and Rich Text export options
You only need to buy one subscription to use the app on all your devices where you are logged with using your iCloud account. There is 7 day trial available.