Pac's have plummeted more than Galaga's
5 yrs ago you could get $180 for a fully tested working Ms.Pac. You would pay about the same for a working Galaga
Now, Ms.Pac is worth about $90 fully working on a good day, while a Galaga will still command about $120-$130 on most sales for tested fully working.
Main reason is that Pac is one of the most well documeted board to repair and most people can easily repair them and most of the chips that fail are socketed or the daughter boards--easily swappable.
Galaga's however primary failures are the resistor packs being broken, or the absolutely horrendous single wipe sockets used that take a lot of work to determine where the failure is. Or of course the thin legged custom namco chips. It takes more time on a less well documented board to fix, even though they are swappable due to dual layers. I think that is why they still have held a bit more value.
If you're lucky you can pick up untested complete boards in the $50-$70 range that MIGHT work or MAY NOT--look very closely. Known dead or visably questionable boards go in the $30-$40 range most of the time for swap/parts material alone... much more than a dead pac these days.