FYI, we’ve just announced pricing of OmniFocus for the Web:
https://discourse-test.omnigroup.com/t/introducing-optional-omnifocus-subscriptions/43509?u=kcase
The full article goes into more depth about everything, but here’s the bit that talks about pricing:
The OmniFocus subscription will cost $9.99/month, giving you access to the web service as well as OmniFocus Pro on all your Mac and iOS devices. If you’ve already invested in OmniFocus 3 and just want to add the web service, the cost for that will be $4.99/month.
These subscription options will be available when OmniFocus for the Web ships next month.