Are you guys freakin serious? It's a ball diamond not a concert hall.

Pick up a used 100 to 500watt 70 volt PA amp with built in mixer, a mic and maybe a source (ie; a cd player) and a bunch of 70 volt PA speakers/horns. Place the speakers where they do the best good now and add to them later as the funds allow. You will have to run 18/2 twisted wiring but tap this line for each speaker on the way.

TOA always made good budget PA gear but there are lots to choose from.