I believe 1/2 pint jellies are about $4.00 each. Sometimes it depends on the lady making them...Just make sure your getting your money back for supplies & time spent making them plus about 1/3 that in profit. Usually thats pretty easy with jellies.
Also check out the freecycle in your area for the jars. I posted last year for canning jars and got over 20 dozen given to me. Of coarse some were full of old stuff and needed to be dumped and cleaned out but free is good.
Also, joining a coupon swap group so that when Ball puts out coupons (which they do a few times a year) you can swap coupons your not using for them. I did this last year & no one on the group I was using used them so I ended up with about 20 coupons. I didn't get to use them all because I just didn't have the money at the time, but once you really get going you can set aside jar money & then buy alot at once. I remember if I had used them all I'd have saved about $50 which was like 5 free cases. I had also shopped around for which store in my area had them cheapest instead of just getting them along with my grocerys.