I don't have a lot of time to put a detailed answer but when talking to businesses about materials and such they will probably help you out by selling it at cost. To them it's a no harm no foul situation because not losing money and can turn around replace it. But before you ask them that ask if they would be willing to donate in exchange for some free advertising. You can make a sign and put it on the fence somewhere. Businesses love free advertising.
End of the day have a parents meeting and ask them who can do what. They may not be able to do it but they probably know someone who does. Most communities want to help out and will help out. The key is getting people motivated and you can't do that unless you ask them. But without sounding like a jerk make sure they understand whatever they contribute it doesn't help their sons gain any playing time.
I say go with a french drain but that's because I have no experience with a sand drain. Definitely check into it though. One question on a french drain is what type of slope is to the field? If you have a slope and don't put the drain in the right spot then you just wasted a lot of time and effort. Rarely does a field set level - it may look level but it really isn't.