Often, the case for a CRM is made in terms of the benefits it will bring to your business. Realistically it's now more of a hygiene factor than ever before, no longer a "nice to have". Companies of all shapes and sizes are using CRM to improve efficiency, target customers more effectively and ultimately close more revenue.
Rather, you should perhaps assess the risks involved with not using a CRM instead. The key risk is that your competitors have an edge over you by using more advanced technology and processes. But you also risk missing out on business due to inefficiency, lack of visibility on key performance metrics, inability to measure ROI.... the list goes on.
The greatest risk in not implementing CRM is that your competitors may have already done it and may be picking up your potential customers. The insight, efficiency, level of customer service and profitability realized through a well-planned CRM system is a game-changer for any small business, so get in the game.