Can I let other small travel agents sell through my portal with their own login and their own price?

Yes, you can. Most travel agency software lets you create sub agent accounts underneath your own account, so another agent gets their own login to the same portal and can search and book for their customers without having to call or email you every time. Every booking they make still sits inside your account, so you can see it, report on it and help with it if something goes wrong.

On price, you normally decide what each sub agent sees rather than showing them your cost. You can usually give one markup to one group of agents and a different markup to another, and the sub agent can then add their own margin on top for their own customer. How finely you can split this, and whether a sub agent can hold a running balance with you or has to pay for each booking as it is made, depends on your plan and on how your payment setup is arranged.

There are limits worth knowing about. Many suppliers require every booking to be made in your agency name, so the sub agent is selling through you rather than holding a contract of their own, and settling the commission between you and that agent is something you handle yourself. Cancellation and refund rules stay with the supplier as well, so you cannot offer a sub agent easier terms than the ones you are given.

Before you open this up, work out how many agents you expect and whether they will pay you before or after travel, then ask for sub agent access to be enabled on your account and test one agent login from search through to booking yourself before you invite the rest.