Remitly "From US bank card" to Thailand bank acct; almost instant (98% of time); fee = $1.99 US; my transfer a couple weeks ago took about 12 hrs for BB to admit it had arrived).
Greatly depends on what the "volunteer" things are. Like taking a car load of locals to visit a Temple and back. Or partly sponsoring a 4.0 student from a very poor family thru college. Providing transportation to a villager needing a round trip visit to a larger hospital 30 minutes away.
My choice would be to wait until I'm in country, then do it. That said, it is still important to determine the issues and rules based upon your home country.
A part of what we see with Imm paper work is to help more Thais have jobs. Thailand goes out of their way to create as many jobs for their citizens as possible.