Another quasi-legal option would be those 49-in-1 or 300-in-1 Jamma board that come up on E-bay and various other sites.
Also - this is a gray area, but I'm not sure what the legal consequences would be of having the games running under MAME itself, if the youth group were non-profit, the machine was set on free-play, and the machine was donated to the youth group . . .
For that matter . . . I am not sure how much of an issue it would be even if it did violate the licenses. I don't want to start trouble . . . And I know (suspect) it is a MAME license violation . . . And I won't publish the company name, but . . .
There is a local vendor selling the Hanaho Arcade PC. It comes with a custom version of MAME and 15 or so Roms. No problem. However - the display machine is also set up with something like MAME32 0.59 and what looks to be a complete set of roms.
I didn't want to stir up trouble, so I didn't ask if the games were included or if they were removed when I bought it. However, even if they were to be removed and the store said that they were only there to demonstrate what could be done on the machine, I suspect that is still a violation of the "non-commercial use" clause of the MAME license, as they are using MAME32 to sell the machine.
And I am just talking about MAME copyrights - (I didn't ask them if they have arcade boards for the 1,000 or so games, b/c frankly I am not convinced that owning the arcade board entitles you to use a copy of the rom from another same model arcade board that you obtained from a MAME set.)