The simple strategy will be to price by the size of the project, something like: small (<5 people), medium (<25 people), large (>25 people).
That said, what you need to pay attention to is how and who will administer the project accounts.
1. It's not uncommon for a project member to leave the project but still act as a SME, come back to the project at a later point, or just come in from time to time to explain what he/she did. So, ideally, you want to keep the idea of people separate from accounts so that an alumni member still has access to his account.
2. Many consulting projects will involve both consultants and client personnel. If the pricing is at the project level, you charge one party rather than billing different parties.
3. If you are running it as SaaS, you have to be very clear who owns what data. While data pertaining to the project is generally owned by the client, any smart consultant will ask for exclusive or joint ownership of system logs (just in case there is any litigation). So separate the project data from the logs.
4. In addition to charging the project, you should include a separate charge for a project admin on your side. This job can become onerous as there will be requests for vpn-based access, active directory integration, managing the accounts of employees who leave either company etc. Think this through since admin can become quite complex.
Hope that helps.