The pricing page that looks cheap per user is expensive the moment you add the freelance designer, the client's marketing contact, and the contractor who logs in twice a month. Per-seat tools charge for presence. Most of those people needed one list, not a workspace.
What a guest is here
Invite someone as a Guest and grant them a single list. They can see that list, comment, and follow the status. They cannot open your other clients, your internal notes, or your rate card. There is no seat to buy. Admin > Security has to have "Allow guests" on; granting the list is a separate step so a guest never inherits a space by accident.
Agencies already run this way
The agencies page is this workflow written out: space per client, folder per engagement, guest on the client's list. The same pattern works for a contractor on a software team who only needs the sprint list, not the whole company.
Compared to paying for the seat
Asana, ClickUp and monday.com all have some form of guest or limited member. The difference that shows up on the invoice is whether the person who comments twice a month is a line item. IterDone's answer is no. The comparison pages spell out the rest: vs Asana, vs ClickUp, vs monday.com.
See a guest list without signing up
The live demo is the fastest way to see the share dialog. No account. Invite-as-guest is the same control you will use on a real workspace.