Many neighborhood and community organizations have funds set aside for things like block parties, or they may be more than willing to pitch in for food, rental tables and chairs or entertainment. Having the neighborhood come together is the goal of good, grass-roots community planning, so enlist help by contacting neighborhood or condo associations.
Local businesses generally love to offer some discounts, giveaways and novelties for the exposure, and restaurants may even set up mobile food service or loan some commercial cookers or expertise for feeding on a large scale. Others may cater at a really fair price.
Larger retailers in the vicinity of the neighborhood might help with discounts and donations, and schools and churches in the area often are subject-matter experts in hospitality. Police, fire and government departments also may have resources for setting up educational booths, sharing food or volunteering manpower. Give them a call and see what falls into place.
If the cost and planning come down to a potluck among neighbors, setting a maximum to spend or making a game out of it, for instance seeing what people can come up with using just $20 and a coal-burning hibachi or the same dish, such as spaghetti or creative hot dogs, keeps it affordable for everyone while adding a game element.