The big ad networks want a cut from business users and will actively suppress posts from business accounts that haven't paid up.

But instead of paying Instagram for reach, consider taking the same budget and spending it delivering samples and coupons to other local businesses mid/late morning. Bonus points if you make the coupons unique for each delivery so you can track which local businesses are your biggest fans. Office managers are generally receptive to this kind of cold call and you can leave a catering menu. Catering gigs can keep your kitchen busy during the off hours.