All peolple have a limited budget and every ecommerce is a story in itself. If you do not know where to start, Google Analytics can give you many useful suggestions.
For example, if you have enough traffic you can invest in SEO, PPC campaigns, traffic comparison engine to bring qualified traffic to your site.

If you have a high bounce rate and a low conversion rate, you can consider many other opportunities such as writing the best keys or changing the product page. You may also seek advice on converting to figure out what to do, or to arrive at a site redesign based on the precise analysis of the customer and the product.

With a limited budget, it is important to prioritize the analysis and objectives and proceed with a plan that includes a step at a time.