If you are willing to spend some time prepping the fruit, fruit trays look better, keep better, are easier to eat, the leftovers are more usable, and people will eat less fruit.
I am hoping you really meant 300, not 3000.
Get seedless watermelons.
Check out the very first fruit tray for 25 on the fruit tray page. Omit the pineapple, add 1 more melon (cantaloupe, honeydew). You would do 10 of these, unless it is the only sweet offering, then 12 would be great.
That page has info on what can be done ahead.
This is about 70 pounds of fruit ready to eat. Plan ahead for the refrigerator space.
The dip can be as simple as fruit or vanilla yogurt with a little honey and mace stirred in.