With the 3 device limit impacting basic accounts where you cannot connect more than 3 devices to synchronise (including mobile devices), some of us need to use a monthly subscription to enable synchronisation to a few more devices. The Dropbox website lists monthly subscriptions at A$15.39 per month (or A$12.74 per month if $152.90 is paid annually) so this actually works out to be quite a bit cheaper at A$13.99 per month when buying through in-app purchases on an iOS device (refer to screenshot from Dropbox app).
Unlike the website (AFAIK), buying through the app gets you a one month free trial, and then if you have been savvy in stocking up on iTunes credit during 15% off sales, this makes the effective monthly price approx $11.89.
I'm aware there was a better deal on Android previously but I have not been great at building up a stockpile of credit, although there may be better deals out there especially if you've been good at completing Google Rewards surveys > https://www.ozbargain.com.au/node/255073
What are the benefits of dropbox compared to onedrive or google drive?