When you compare the exposure you get from Shareasale to the cost of other large networks... CJ, LinkShare, etc. You'll find their fees are very reasonable.
The Better question is if it's a good platform for your project. Are there any other companies in your niche using Shareasale?
I promote a lot of products, and I'm a huge fan of Shareasale as an affiliate. Easy to join, good tools, on time payment. So from an affiliate perspective it's very attractive as well.
Keep in mind that affiliates can see what is performing... just like CJ so after time if your products are not selling this could work against you. But this is the case in nearly all networks now.