Lifetime Mac

Buy once instead of Dropbox

Dropbox Plus costs
$120a year. 2 TB Plus on annual billing; $11.99/month if billed monthly. Their pricing
Ways out
2apps that do the same jobs
Cheapest to buy
$49.99ChronoSync, which pays back in 5 months
Cost nothing
1freeware or open source

Read the catch on each before you switch. A one-time price is not automatically the better deal, and we say so where it is not.

2 apps
SyncthingPeer-to-peer folder sync with no cloud, no account and no quotaFreeOpen source

No official Mac app — you configure it in a browser, and the menu bar wrappers are third-party

ChronoSyncDefined, repeatable folder sync jobs with free major upgrades$49.99Perpetual

Syncing to another Mac properly wants ChronoAgent, a separate $19.99 purchase