If you have to pay to volunteer, it’s not employment experience, it’s tourism. No one cares about tourism on your resume. It’s also no particularly useful to the organization – beyond the fee you pay. If your work was useful, they’d pay you.
If you want to go on vacation to a poor country, go. Choose locally owned hotels and restaurants. The money you spend will benefit the economy.
If you want to donate to an organization in a poor country, do that. There are lots of great ones to choose from. (I’m on the board of Oceanswell, and I know the founder of Cando. I can vouch for both of them)
Don’t conflate the two. Spending your vacation carrying lumber eliminates a job that could be done by a local person for pay. Playing with orphans is actually harmful to them.
The exception: the UN Volunteer program.