I think saying "sell it" is stupid advice. It doesn't sound like the business has popped an artery.
What I've learned from business owners is that if you start with one advertising medium (Like flyers you just said), you have to be committed to do it for at least 6-12 months, or its a waste of money. For example, if you have a sign on the street for one day, people will see it, but if it is up for only one day and the same people drive pass the same street, they will forget your business exists. Whatever advertising you do, you must keep it going for extended periods of time to get your business & what it offers IMPLANTED in their mind. If your sign is up everyday they drive down their same street after work, your business is engraved in their head, and when they finally NEED your service they will go "Oh, I remember that one Party Store".
I agree 100% with what Advertise Here said.
Maybe instead of selling it and moving to 100% internet, you can open an online segment of the business and that way you can expand the business without creating too much more overhead exp.
What are your advertising expenses as a percentage of total sales?
A Quitter never wins, and a Winner never quits.