I've recently cut down to one or two cups a day, and I'm not super picky, so I'm not the target market here, but I'll give my two cents anyway in case it helps.

Number one, $19 for 8 cups of instant coffee seems really expensive. I can get a really good basic coffee around here (Boulder, CO) for between $1.50 and $3, depending on size and quality. If the instant costs almost as much, I might as well just walk across the street.

Second, a subscription model seems strange for instant coffee. It's something I'll use when I don't want to make regular coffee, but also can't run across the street to buy one. I'm not in that position often, and I'm not even a coffee snob.

Just a random thought, but have you considered a tiered approach? Sell the first extraction at a higher cost, but also have a cheaper product line that does the extraction process two or three times to increase the yield?