With a book signing, the author is on hand to sign the books in person. For them, it's much-needed publicity. In turn, they help generate interest in, and attract business to, your shop.

You asked about a low-budget service that would suit a book shop. Books are a very popular gift. You could have a free gift-wrapping service. Anything that makes it more convenient to buy is going to help increase sales. Make sure to promote your service and that includes having something in the window for busy passers-by who need to pick up a gift on their lunch hour.

Another service you could offer is a locator service for rare and out-of-print books. As long as you could do the research yourself, it would definitely be low budget since it would be basically a matter of your time.

Good luck with your business.

Nancy
http://www.CreateYourMarket.com
Marketing Ideas for the Home-Based Entrepreneur