Retailers often ask me how much they should charge for shipping. Retailers often tell me that they'd like to make money on shipping, or at the least not lose any.
I'd remind retailers that many large retailers are losing money on shipping. In this super competitive environment, just getting the sale and a new customer are the goals.
As an example, please see this article about amazon.com and Walmart competing to offer super low shipping fees. Walmart traditionally requires a minimum purchase of $35 to receive free shipping.
The article also states that Walmart offers a $50 subscription service whereby one receives free three-day shipping. This helps it compete with amazon's Prime service.
My recommendations are to a) follow Walmart and amazon and offer a subscription service offering lower shipping rates, and b) in general lower the threshold which qualifies a purchase for free shipping.