Most people need to earn an income to support themselves. Thus you probably need to consider part-time contributors. Which in turn might require considerable project management skills to ensure that substantial units of work can be accomplished by teams of people.

Not all FOSS projects are purely by volunteers. Many contributors are actually employed to work on those projects part-time or even full-time.

With that said, I think that often the issue with volunteering is that it feels too much like work, that is, the emphasis is placed on some abstract goal (finish X thing) vs the why (by finishing X we’ll be able to help Y people!)

I also think that working with volunteers is interesting because one has to also worry about how they find value in what they are doing. There are a bunch of valuable things apart from money like community, belonging, purpose, doing something bigger than one self.

Hopefully this disparate collection of thoughts and ideas makes sense :)

PS. Email is on profile, feel free to reach out, I’ve been on the look for technical volunteering opportunities :)

Just pay for professionals because that's how you insure stakeholder buy-in for the project. Is this something donors expect you to be spending time on? Have the executive team green lighted the action? Budgets are always a bright line test.

If not, then there is a good chance a volunteer is wasting their time...and worse, you will be wasting a volunteers time simply by not valuing it. People smell that pretty quickly.

If you want professional work, hire professionals. Good luck.