Salesforce offers non-profit access FREE for 10 users or less:
Go to https://www.salesforce.com/company/power-of-us/ (or equivalently https://www.salesforce.org/power-of-us/)

Steps:

1. Log in to the Power of Us portal to submit your application. Have your Tax ID Number and legal documentation ready — a 501(c)(3) or 501(c)(4) IRS determination letter in the U.S., or the relevant tax document for your country. Salesforce
2. A Salesforce org or trial is not required to complete your Power of Us application — just apply and you’ll be provisioned a Salesforce org with your licenses. Salesforce
3. Once you receive an approval email (typically 2–4 weeks), log back into the Power of Us Portal with your Trailblazer profile to select your product.
4. Once approved, organizations can request one of two license bundles: 10 Agentforce Nonprofit – Enterprise Edition licenses, or 10 Sales and Service Cloud – Enterprise Edition licenses. Salesforce Ben If you choose the Sales and Service Cloud option, you can still manually install NPSP on top of it.