You've forgotten that non-store listings only run for a maximum of 10 days, whereas store listings run for 30 days.

To do the maths, even IF you got 290 freebies in a month (which is definitely not the norm), that equates to 2,900 "listing days" if you can't get AR.  A store gets 200 x 30 = 6,000 listing days, which is more than double the exposure.

If you don't feel you're getting enough sales to justify paying $19.95 every month, only you can decide whether to keep the store or to reduce your number of listings and their exposure and perhaps get even less sales.  It all comes down to what you're selling and how much you need to get rid of it, and how much you rely on the money from it.