I'm in Plano TX area and the little signs on the corners are a big no no and if you continue to do it you will be fined.
That said...I don't know the nature of your business but most of the time, schools are looking to raise money and they get people to advertise in the directory, donate and advertise for fundraising activities. Our HOA has a website and you purchase advertising. I'm involved with the cheerleader booster club and our main fundraiser if making/selling the football programs. We sell ads for the programs. All of these avenues are reasonalbe as far as advertising costs to you.
Word of mouth is the ultimate fantastic (FREE) advertisement for you.
We run our company from home but it is in such a niche market, we do no advertising at all. Our customers have been referred to us in most circumstances.
Good luck.